All of the Mercedes-Benz E-Class cars are enjoyable to drive. Smooth, serene and quiet are the dominant impressions at the wheel of any E-Class, unless you have the accelerator floored. There's very little vibration anywhere in the cabin, and almost no wind noise.

Improvements to the geometry of the front suspension for 2007 has given the E-Class a crisper, quicker turn-in while cornering, perceptibly increasing the sporty nature of the car's handling. All of the E-Class cars corner responsively and provide a smooth, if slightly firm, ride, a balance we like in luxury sedans. The four-link front suspension is similar to that under the expensive S-Class models, and the five-link rear suspension does a superb job of controlling unwanted wheel movement, which is crucial to handling and ride quality.

The variable-power steering system was improved for 2007 with a 10-percent quicker ratio for more precise control of front wheel direction. The system provides more boost for easy turning at low speeds and less for more progressive steering response and feedback at higher speeds. With 2.6 turns lock-to-lock compared to the previous system's 3.3 turns, we found the new steering makes maneuvering through crowded parking lots easier and more pleasant, and it's far more responsive in the corners.

The Sport models are tuned for those who like to feel in closer touch to the pavement, as they are fitted with shorter springs for a slightly lower ride height, stiffer shocks, and low-profile performance tires on 18-inch wheels.

On V8 models, the Airmatic Dual Control suspension replaces the standard steel coil springs with air springs. This computer-managed system adjusts the air pressure to the spring at each wheel, based on road conditions or driving style, to slightly soften or firm the ride and to add or decrease body roll (lean) in corners. In combination with electronically adjusted shock absorbers, the air suspension can automatically improve ride quality or handling or optimize the balance of the two, depending on where the car is traveling and whether the driver is cruising or driving quickly. The system works automatically, without switching suspension settings between sport and comfort.

The previously touchy brake system was simplified for 2007, and now provides an ultra-smooth grasp, even at slow speeds. Each E-Class model has progressively larger brake rotors and more complex piston designs to complement the engine's power and corresponding speed potential. The E-Class wagons give up almost nothing to the sedans in performance, fuel economy or handling dynamics.

The E350 comes with a 3.5-liter engine, the first Mercedes V6 with dual overhead cams and four valves per cylinder. The 3.5-liter V6 generates 268 horsepower, and it mates well with the high-tech seven-speed automatic transmission that comes standard. The E350 is as responsive as any V6-powered car we've driven. This engine also features fully variable valve timing, so it delivers an impressive amount of torque from idle all the way to redline. The E350 responds immediately, no matter how fast it's already traveling when the driver dips the gas pedal. The 3.5-liter engine is also appreciably smooth, particularly at high rpm. And thanks to the seven-speed automatic, it delivers decent fuel mileage.

The E320 Bluetec diesel gets vastly superior fuel economy, with EPA ratings of 23 city/32 highway mpg. With predominantly highway travel, this gives it a range over 600 miles per tankfull. The Bluetec is designed to run on the ultra-low-sulfur diesel fuel introduced into the U.S. starting October 2006. Mercedes' first V6 diesel, the Bluetec features all the latest high-tech goodies, including turbocharging, a variable nozzle turbine, four valves per cylinder, exhaust gas recirculation and a third generation of CDI, the common-rail direct-injection system that delivers fuel to the engine at an incredible 23,000 psi (compared to 100-250 psi in a typical gasoline engine).

Yet the technology matters less than the results. The diesel V6 puts out a modest 210 hp, but is backed up by a resounding 400 pound-feet of torque that begins as early as 1600 rpm. In other words, this baby hauls. There's no smoke to be seen or smelled. Four after-treatment units in the exhaust stream help make the Bluetec V6 the cleanest diesel powerplant in the world. Initially, the Bluetec was sold in 45 states only, but Mercedes-Benz expected that a further evolution of Bluetec will allow diesel Mercedes to be sold throughout the United States in 2008.

We drove the E320 Bluetec sedan through the deserts and mountains surrounding Las Vegas, and it exhibited all the attractive traits of the gasoline-powered Benzes, and more. As well as being as smooth and quiet as any of the world's luxury sedans, Bluetec comes with a powerful character all its own, owing to the massive yank of torque that pulls the car from 0 to 60 mph in just 6.6 seconds, only a tenth of a second behind the gas-powered E350 sedan. In other words, forget everything you know about diesel-powered cars built in the 1970s, '80s or '90s. Slow starting? Not anymore. Like all diesels, the Bluetec still needs electric glow plugs to heat the combustion chambers before starting, but we never noticed.

Unpleasant odors? You'll still experience that oily diesel smell at the truck stop when you fill the E320 Bluetec's tank, but once the filler cap is back on and the car is running, there will be no unpleasant fumes inside or out. Excessive engine noise? At idle, during warm-up, we heard the rapid tick-tick of diesel noise more loudly than anything coming from the gasoline-powered E350's engine, but once underway, there was zero difference in the amount of engine noise reaching the cabin compared to other E-Class models. That extra bit of noise is more than offset by the Bluetec sedan's excellent benefits.

With 400 pound-feet of torque, more even than the E550 boasts with its V8, the turbodiesel V6 makes a winner of the E320 Bluetec in almost any stoplight derby. The 3,860-pound sedan, though no lightweight, jumps forward quickly enough to spin the back tires just by jabbing the right pedal, if you've switched the traction control off. Its turbocharger also provides a level of immunity from the power-robbing effects of high elevation, as we discovered in our climb up Mount Charleston northwest of Las Vegas. And on one quiet desert road, we reached the electronically limited top speed of 130 mph without breaking a sweat.

That said, there's nothing like the E550's V8 power for smooth, exhilarating acceleration. This V8 is sweet from idle to the 6000-rpm redline, and with 382 horsepower and 391 pound-feet of torque, the E550 flies. From a stoplight or from 70 mph, there's a deep well of torque underfoot and plenty of acceleration, good enough to rocket from 0 to 60 mph in 5.4 seconds. Throughout our first drive of the E550, on the high-speed autobahns of Germany and over the twisting roads of the Bavarian Alps, it provided a stellar combination of performance and luxury, sharp handling and passenger comfort. In short, the Mercedes-Benz E550 is as nearly perfect a sports sedan as has been developed by anyone.

The seven-speed automatic transmission improves acceleration, performance and response, but it also enhances fuel efficiency when compared to a more common five-speed automatic. Gear changes are barely noticeable, especially in the higher gears. This transmission allows significantly quicker acceleration for highway passing situations. And it doesn't have to go through every gear: Step on the gas and the transmission will skip down to the appropriate gear, switching from seventh to fifth, for example, and from there directly to third, meaning two downshifts instead of four. Both this transmission and the five-speed also offer three individual driver-selectable shift programs to alter the shifting characteristics from comfort to sport to full manual gear selection.

The E63 AMG sedan and wagon operate on another plane entirely. Their race-bred naturally aspired 6.2-liter V8, which replaces the supercharged E55 V8, is now being offered in a variety of Mercedes models. The new big V8 delivers 507 horsepower and 465 pound-feet of torque, and catapults the E63 models form 0 to 60 mph in just 4.3 seconds.

The 6.2-liter V8 is the first Mercedes engine to be totally engineered and built at the AMG facility, and the firm put every bit of its long motorsports experience into it. The all-aluminum engine features four valves per cylinder, a variable intake manifold made of magnesium, variable camshafts and a special low-friction cylinder wall treatment, but the most important part is it performs and growls like a big V8.

The E63's transmission is an efficient seven-speed automatic with AMG-tuned Speedshift programming. It shifts quickly up or down (though without the throttle blip of some manu-matics), doesn't hunt back and forth for the right gear, even in hilly terrain, and it rarely shifts unless the driver changes the angle of the gas pedal, which is good. When the driver prefers, an auto-manual shift mechanism allows a high level of control over gear selection. Either by toggling the shifter left or right or using the paddles on the steering wheel, the transmission shifts quickly up and down at the driver's discretion. The system will hold the selected gear indefinitely just below the 6000-rpm redline, but it won't let you bump the engine off its rev-limiter without shifting up a gear. Should the mood strike, a driver can run through the gears or challenge a curving stretch of road almost as if it was a fully manual transmission. Drivers who like that sort of thing might gripe about the lack of a blipped throttle during downshifts like some other transmissions of this type deliver, but that's a minor point that will be moot to almost everyone else. Most of the time, we simply left it in Drive. Even the high-performance E63 AMG is so quiet that the driver forgets just how powerful and fast it is until the throttle is opened up.

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