Look back over the 100-plus years of automotive history and you'll find a relative scarcity of 12-cylinder cars. Nothing speaks of high end motoring more convincingly than the vaunted V12, but due to cost and complexity, they've never been all that common outside racing.

Originally developed in airplanes, after World War I, V12 engines powered luxury cars from makes like Cadillac, Packard and Rolls-Royce (all of whom also built airplane engines). Packard's 1912 'Double Six' is regarded as the first automotive production version.

Post-WWII, 12-cylinder powerplants became obsolete for most practical purposes, and virtually disappeared from the landscape. Through the '50s and '60s, V12s almost exclusively powered GT sports cars, first from Ferrari, then Lamborghini.

BMW is reputed to have developed a V12 in the early 1970s, but in the light of fuel supply crises, the project was deemed economically irresponsible. Jaguar was not so easily deterred, mass-producing a V12 for the E-Type, beginning in 1971. Jaguar was also the first manufacturer in some three or four decades to resurrect the V12 in a four-door sedan, the XJ12, 10 years later. Both car and engine were discontinued in 1997, but by then the two German juggernauts had developed their own contemporary V12s, BMW for real in 1986, and Mercedes-Benz in 1991.

The BMW and Mercedes sedans continue to use proper V12s, the 760Li a naturally aspirated 6.0-liter, the S600 a twin-turbocharged 5.5-liter. The Audi and Bentley run Volkswagen Group's W12, introduced in 1999. Unlike a V12 with two opposing banks of six cylinders, the VW W12 is arranged in four three-cylinder banks; in simplest terms, two conjoined VR6 engines.

Why the hype? Twelve-cylinder powerplants offer three things: superfluous power output, and preternaturally smooth and quiet operation due to perfect primary and secondary balance-both important in an executive sedan. And of course, there's bragging rights. Each manufacturer represented here has a vested interest in 12-cylinder technology, having been instrumental in its historical implementation, both in racing and on the production line. Simply having the capability of developing and supporting a 12-cylinder engine is reason enough to offer it, and damn the expense.

But of course, these sedans are as much about luxury and comfort as power. Each is filled with all the niceties and high-end technical trimmings you'd expect in a flagship model. So we found ourselves spending as much time playing with multimedia systems and adjusting seats as driving.

The Audi seems to be everyone's sentimental favorite. Maybe it's because I'm associated with so many Audi geeks. Or maybe it's the company's bold vision of kicking the crap out of the premium-brand establishment. Whatever the appeal, Audi has been hard at work rebuilding and reinforcing its image as the viable luxury alternative. And in that sense, the new A8 is nothing less than the defining product.

Driving the Audi is an incredibly civilized event. It is well planted and urges confident acceleration and cornering. But like other Quattro cars, it suffers from steering that doesn't feel entirely alive. The naturally aspirated W12 is well powered, but acceleration is more relaxed than stupefying. Still, it feels at least as quick as the twin-turbo Bentley; although it's about 100 hp down in power, it weighs more than 700 pounds less.

Of the group, I find the A8's shape the most appealing, more powerfully defined yet simultaneously more sleek and streamlined than the other three. The inverted trapezoidal grille has become the most iconic automotive face on the road, and no Audi wears it more convincingly than the A8. The 20-inch wheels, a $3,200 option with summer tires, are particularly striking and hearken to Audi's high-performance RS line.

Like the exterior, the interior design is clean and well drawn. Buttons and controls are intelligently arranged. It is at once more engaging and inviting than the obtuse 760Li or the somewhat cold S600. And the Audi definitely has the best multi-media and entertainment systems. On initial entry, the MMI interface is probably the most easily deciphered cabin control system, comprised of a multi-function knob and four buttons which correspond to the various sub-menus on the central LCD screen. It's about as black-and-white as these things get. The cabin's rear portion is cavernous-the most legroom of the group-and incorporates its own dash console featuring dual auxiliary inputs, two sets of Sennheiser headphones, and LCD screens in the front-seat headrests. If you're going to ride in the A8L, you probably want to be in the back, though the seats aren't quite as comfy as those in the BMW or Mercedes. And the DVD changer is located in the trunk, so it's not accessible in transit. That sucks, but the whole system is listed as standard equipment on this model, which is great. This car is also equipped with the Bang & Olufsen sound system, a $6,300 option sure to impress audiophiles.

The Flying Spur is unique in that it's the only car on the panel representing the manufacturer's lower end. To move upmarket, you'd have to opt for the V8-equipped Arnage (and spend around a quarter million bucks doing it). Elitists may look down their noses at the Bentley that Volkswagen built, but it's hard for most other mortals to deny the Flying Spur the respect it is due.

With a reported top speed of 195 mph, there's little doubt the Flying Spur is fast, but it doesn't feel exceptionally quick. This isn't because it's not powerful-it's got 550 horses after all, and a load of torque-but it's also more than a quarter ton heavier than any of the other three cars. Turning triple digits is as leisurely an experience as getting in and buckling your seat belt. This car doesn't bury you in the seats-it gently eases you back as its inertia builds. Keep your foot in it and the implications are frightening.

This particular Spur comes with the Mulliner specification, which adds nearly $9,000 to the price and includes, among other things, diamond-quilted stitching to the seat surfaces and door panels, drilled sport pedals, a knurled-chrome-and-hide gear lever, and 20-inch two-piece wheels.

The interior is truly a masterpiece, every inch speaking of artisan craftsmanship. Ours wears a snazzy 'Hotspur' red-and-black color scheme wherein opposing red and black sections are meticulously hand-stitched with black or red thread, respectively-a small but striking detail. Bentley says it takes 11 cowhides to provide leather for a single interior, and sure enough, nearly every surface is skinned in leather, including the perforated headliner. In spite of its latent haughtiness, the cabin is a wonderful place to spend an afternoon, though the bench-style back seats do leave something to be desired compared to the bucket-like BMW or Mercedes rears.

While by far the most expensive ride in the group, the Flying Spur has a relative lack of bells and whistles compared to its 12-cylinder peers. Rear passengers benefit from walnut 'picnic tables' which fold down from the backs of the front seats. Those would set you back $2,100, but this car is equipped with no multimedia to speak of beyond the DVD navigation. A rear entertainment system would have been nice, but hell-it remains a Bentley, with all that entails.

The 760Li is the best driver's car in the group. BMW has an odd knack for making its big cars feel and drive much smaller than they actually are, and it's particularly evident in this biggest and heaviest 7 Series. The 760's steering and suspension, both very good, maneuver it more like a sport sedan than a limousine. I guess that's core BMW for you. Power delivery, while not as phenomenal as the Benz, is good, but in a typically subdued manner, not unlike the two W12s. The transmission's lazy full auto mode can numb the experience. But if I needed to chase someone up a mountain pass in one of these cars, the BMW would be it.

Its interior, however, is the biggest let-down. The color is bad, sure, but most disturbing is the copious use of plastic. For a car priced comparably to the A8L, the 760Li lags terribly behind the Audi in trim quality.

And some of its ergonomics are a little clumsy. The front seat adjustments are not particularly intuitive to find and use. Worse are the steering wheel transmission controls. The 760's six-speed has full auto, sport auto and manual modes. In manual mode, you control gearshifts with a pair of buttons located both on the wheel's face and its backside. The intention is that you control downshifts with your thumbs (wheel face) and upshifts with your index or middle fingers (wheel backside). It's just weird. I couldn't really reach the buttons with a comfortable grip at nine and three, so manual shifting was not particularly convenient. I don't see why BMW can't just use SMG-style paddles.

Our 760 has a flip-up LCD screen for the rear passengers, with DVD and iDrive capability. The official list of options details the DVD changer in the trunk, but there's also a pop-out magazine in the front dash and another in the center console. And while it is an option for the others, this 760 was the only car of the four fitted with a cool-box placed between the rear seats.

Speaking of seats, once you master the adjustments, they offer a reasonably wide range of fine tuning, ranking somewhere just behind those of the S600. The iDrive interface continues to be a bit of a pain in the ass, more apt to induce a migraine than the COMAND or MMI interfaces on the Benz and Audi, but like they say: practice makes perfect. You'll figure it out eventually.

The fact that it's from a car company in business for longer than any other should at least say something. The S600 is a magnificent vehicle derived from a long and storied lineage of magnificent vehicles. I can't say I particularly like its new look, but I won't dwell on it. Beneath the sheetmetal lies the most well-rounded sedan in the group.

The S600 is the only car here I'd say feels genuinely fast, thanks to massive torque output, peak of which is available beneath 2000 rpm. Prod the accelerator at any speed and the car launches forward enthusiastically. It achieves 60 mph in just 4.5 seconds-sports car territory, and an average half-second faster than the other three. It's impossible to keep your foot out of it-until you go to fill up the 20-gallon gas tank.

The Mercedes feels good on the road, perhaps not as hardwired to the pavement as the BMW, but well mannered and surprisingly controllable. The steering is light for my taste, but precise at speed and effortless in its actuation.

Some may find the interior a bit cold, but it's the cleanest design. Basic controls are arranged in a single arc of chromed switches across the center dash. These functions can also be adjusted through the COMAND dial, which ranks between the BMW's iDrive and the Audi's MMI according to ease of use.

The seats are above and beyond anything else in the automotive realm. You can adjust them with the standard door-mounted cluster, but to really dial them in, press a button in front of the COMAND dial for a graphical display that allows you to tweak each individual section just so. The range is amazing: shoulder and backrest tilt, thigh and lateral bolsters, shoulder, thigh, and lumbar supports, seat height and tilt, and on and on. You don't just adjust the seat-you literally ensconce yourself within it.

There's also heat, cool, or massage, and best of all, active lateral bolsters that engorge to support your 'slide side' during cornering or lane-change maneuvers. The back seats, while not quite as customizable as the fronts and lacking the dynamic bolsters, have the greatest range of adjustment among the four cars.

One feature conspicuously absent on the Benz, present in the other three, was keyless entry and ignition. It is available as an option, but it might as well be standard at these prices. This S600 also lacks multimedia entertainment for the rear seats. Even without these things, I'd have to say the Mercedes is my favorite. Everything considered-road manners, power delivery, comfort, build and material quality-the S600 has it all, and it's all good.

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