These quintessentially American vehicles, based on pickup truck platforms and powered by voracious V-8 engines, seem like creatures from another era. At a time of economic distress, they symbolize Americans’ predisposition to over-consume – buying vehicles we want rather than vehicles we need. With their enormous weight and insatiable appetite for gasoline, they are definitely not cool anymore.

Yet there are times when the sight of one of these monsters sitting in your driveway is comforting, and there is nothing else you would rather drive. Take the weekend before Christmas, when the temperature in my neck of the woods dropped into the single digits and successive snowfalls left a foot or more on the driveway.

After I climbed into the Chevy Tahoe hybrid, the engine cranked immediately, without hesitation. Even though snow covered every window surface, spending a few minutes warming up the cabin and running the front and rear defrosters was no burden because the wide-open interior spaces induced no claustrophobia.

When the time came to put the car in gear and get it rolling, the on-demand four-wheel-drive pulled the truck effortlessly through the snow. On the road, there was nothing to fear from slush thrown up from passing vehicles because we sat up so high, the windows were never blocked.

My only concern was the large front spoiler that hung down from the front bumper, making it easy to clog with snow or dent in a parking lot snowdrift. Nothing worrisome materialized, however.

The Tahoe also proved its worth hauling household goods to and from New York City on back-to-back trips. Its carrying capacity is significant and the abundance of creature comforts for the driver – such things as seat heaters and satellite radio – kept fatigue and boredom to a minimum.

Where the Tahoe falls down is on the value side of the equation. A couple of thousand dollars of options like the rear-seat entertainment system and a $950 delivery charge pushed the as-tested price up to $56,500 – though beleagured Chevy dealers will surely sell you one for thousands less.

And the electric motor that turns the Tahoe into a hybrid did little to slake its thirst for gasoline. The hybrid Tahoe is rated at 20 miles per gallon by the EPA, vs. 16 mpg for the standard one. I was able to get only a little better than 19 mpg over some 400 miles of driving.

The hybrid Tahoe was a welcome weekend houseguest guest during some especially inclement weather, but I’d have a hard time finding room for it to move in on a full-time basis.

For a long time, diesel has reminded me of Brazil: It is the fuel of the future – and always will be.

Recent events seem to prove that out. Just when German manufacturers have begun to offer clean diesels that meet emission standards in all 50 states, the price of gasoline has plummeted and widened the value gap with diesel fuel. You’ll be burning fewer gallons in your diesel-powered car, but you’ll probably be paying more for them. So you can’t recoup the extra cost of the heavy-duty diesel engine with improved fuel economy.

With those thoughts in the back of my mind, I tested two diesels on back-to-back weekends.

The specifications for the 2009 Jetta TDI got me excited. Here was a German sport sedan (albeit one built in Mexico) with a sophisticated turbo-diesel engine, and bearing a sticker price under $25,000 ($24,190 to be precise).

As promised, the Jetta’s fuel economy is impressive. EPA figures a combined average of 33 miles per gallon, while some drivers say they can approach 50 mpg. There is no free lunch, however, and the Jetta TDI exhibited some flaws. I heard the distinctive “diesel clatter” when the car idled – not a disruptive sound but not desirable either.

More disturbing was the pronounced turbo lag; the better part of a second was required before depressing the accelerator resulted in a noticeable surge forward. It wasn’t the smooth pickup I was hoping for.

Neither of those problems was apparent in my second diesel, Mercedes’ 2009 ML320 BlueTEC. The engine was as quiet as any car I’ve driven, and its performance was as seamless. A well-sorted Mercedes exudes a confidence and sophistication like no other, and this body style has been in production long enough to have its rough edges buffed out.

Once again though, I came up empty-handed trying to find a clear rationale for choosing a diesel over a gasoline engine. The city/highway mileage of the diesel ML is rated at only 18/24, which is not a huge improvement over the gasoline-powered ML’s 15/20.

And I still haven’t adjusted to the aggressive pricing of German luxury cars. While the base price on the ML was tabbed at $48,600, entertainment and heating packages – along with some other geegaws – rolled it up to $58,885. It is hard to feel green with that much precious metal under your foot.

Diesels continue to be a huge deal in Europe, where taxes keep the price of diesel fuel closer to that of gasoline. And they will get a lift in the U.S. next year with the introduction of the Honda Accord diesel. Hopefully, that will be enough to move them from the future back to the present because, based on my recent experience, they aren’t there yet.

For years, Toyota has been rudely stereotyped by car buffs as unimaginative and its cars as dumb-downed and boring. But you can actually make a case that Toyota – along with Honda – is the most innovative car company on the planet.

To cite two recent examples, Toyota pioneered crossover SUV development 12 years ago with the RAV-4, and it has single-handedly made gas-electric hybrids the preferred alternative to the internal combustion engine.

Toyota’s latest idea, the Venza, isn’t in the same league – it is a niche vehicle with a conventional powertrain – but it is worth paying attention to all the same. With four doors and a hatchback, the Venza’s roof is lower than an SUV’s (like a Highlander) but higher than a station wagon’s. Combine that with increased ground clearance, an athletic stance and all-wheel drive, and you have what Toyota calls a “crossover sedan.”

The Venza was dreamed up in Toyota’s California sales office as a car for empty nesters who didn’t want all that SUV space any longer but appreciated SUV versatility. After intensive vetting by Toyota product planners, it was approved for production four years ago.

Since it is a Toyota, it has been cleverly engineered to reduce investment: Only one-third of Venza’s parts are new, and the remainder come from the Camry sedan and Highlander SUV. The Venza will also be built in the same Georgetown, Ky. plant where those cars are assembled.

I was initially skeptical about the Venza’s mixed heritage – it is hard to turn a mutt into a purebred – but it is a car that you have to see in the metal and drive on the road to fully appreciate. All the design elements – the prominent grille, high roof and sloping back – work together elegantly, rather than awkwardly, and the entire body is beautifully shaped.

Inside, the materials and fittings are Lexus quality, equally elegant to the eye and the hand. It is no surprise that Toyota ranks above all other mainstream brands in perceived quality, according to Automotive Lease Guide. Underway, the Venza feels as slick as a Lexus too, smooth and powerful.

Toyota has learned what its reputation is worth in the marketplace, and the V-6 powered bronze Venza prototype I drove carried a sticker price of $36,735 plus $720 for delivery/processing/handling. As a looming empty-nester myself, I discovered that the Venza might be more car than I’d need – but perhaps one that I’d want.

The red-over-black GT-R squatted in my driveway like an angry beast from another planet. No graceful shapes or elegant curves disguised its blunt purposefulness.  This is the car designed, first and foremost, to beat all other production models around Germany’s famed Nürburgring.  Whether it does or not, it lives up to its nickname “Godzilla” even when parked.

Which would be fine, except that I live in northwestern Connecticut, and, despite the proximity of Lime Rock Park (“Roadracing capital of the East”), I almost never get an opportunity to evaluate the full potential of a 480-horsepower car that can claw its way to 60 miles an hour in 3.9 seconds (without launch control) and claims a top speed of 195 miles per hour.

What I could do was make some short loops around town and then log 150 miles at higher speeds on the Massachusetts Turnpike. What I found was that this is not a car you would choose to make a leisurely morning run for the New York Times and a cup of coffee.  That’s mainly because first gear in an all-wheel-drive car with the power of the GT-R has all the subtlety of a stump-pulling tractor, heaving and jerking as it translates the immense horsepower into forward motion.  Second gear in the dual clutch, paddle-shift, six-speed transmission was lots smoother,  but you needed to get up a little speed before the computer brain behind it would allow you to get there.

Nor does the view from the driver’s seat give you much to warm up to.  The cockpit has all the ambiance of an F1 racer, with surfaces and instruments designed more for practicality than esthetics, purpose  not pleasure. This is not a car for lounging in.  One thoughtful touch is the addition of two rear seats, suitable for pets, small children, and masochistic adults – an unusual  concession to practicality.

But although the GT-R is designed to be a daily driver and carries a relatively modest sticker price of $72,000, it is as finicky in some ways as an exotic.  Specifically, the alignment tolerances are so narrow that a minor irregularity can throw the wheels out of whack.  My GT-R shimmied regardless of the road surface, requiring constant corrections of the steering wheel.  I was informed that it needed a wheel alignment after only a few thousand miles of use.

With those caveats, the GT-R lived up to its advance billing as one of the most technologically-advanced,  high-performance cars in the world and is ably performing its task of raising Nissan’s profile. GT-R owners form a very exclusive club – the purchase of only 321 cars was transacted in November, but enthusiasts have gone bonkers over it and Motor Trend voted it car of the year. For me, however, the GT-R is a car more to admire than to love.

Among the three German luxury car companies, Audi is standing tall. It is raising its U.S. profile, advertising more aggressively and enjoying strong sales. By adding to its lineup with sporty models like the A5 and S5, it has significantly freshened its image. While BMW sales are off 10% this year and Mercedes is down 5.3%, Audi has fallen just 3.5%.

The core of the Audi lineup is the compact A4.  It competes against the BMW 3-series and Mercedes C-class, and accounts for more than half of Audi’s U.S. sales.  For 2009, the car has been widened and stretched,  and it has been given a sharper-edged, more tailored look. It’s Audi’s first all-new platform in more than a decade.  In all, the 2009 Audi A4 is 4.6 inches longer than it used to be and a full seven inches larger than BMW’s 3-series. The main beneficiaries of the extra length are rear-seat passengers who, if they can’t stretch out in business-class style, will at least not have to ride with their knees under their chins.

The A4 comes with two engine choices: a 3.2 liter six cylinder and a 2.0 liter turbocharged four.  I tested the four and it at no time left me wanting for more power.  Good thing.  The base price on my Brilliant Red tester was $32,700 – not far from the $33,400 entry fee for a 3.0 liter BMW 328i that has two more cylinders.  Add on $7,300 for the ”prestige model” (18” wheels, premium sound system,  chrome window trim), $2,500 for the navigation package with rearview camera, and $3,350 for some other goodies plus destination charges and the as-tested price for the A4 jumped to $46,675. That’s a healthy bite for a four-cylinder car.

Price aside, the A4 lived up to my expectations in every way.  The refined and sophisticated cockpit with its easily accessible controls should be a model for all other automakers.  Dynamically, the Audi was flawless, with impeccable steering, handling and ride.  With its three settings, Audi’s adjustable suspension provides just as much comfort or control as you’d like  – and unlike systems on other cars, you can actually feel the difference when you change between them.

Most  luxury cars are for extroverts, but Audis are aimed at the inner-directed.  A weekend’s worth of patrolling the back roads of car-crazy Litchfield County (near Lime Rock Park race track)  elicited no thumbs-up or other spontaneous gestures of approval.  That’s fine.  Traveling beneath the radar has always suited my personality, and it cuts down on speeding tickets. If the euro continues to weaken and Audi can adjust is pricing accordingly, its appeal will only grow.