Perhaps no luxury sedan has ferried so many celebrities, foreign dignitaries and well-to-do professionals as the Mercedes-Benz S-Class. In recent years, this flagship four-door, with its über-luxurious interior, brand prestige and host of high-tech options, has been one of the finest luxury sedans one can buy short of much more expensive options from Bentley, Maybach or Rolls-Royce.

Although the 2009 S-Class has a bulky curb weight to match its imposing street presence, any of the available engines can pull the sedan's weight with ease. From a 5.5-liter V8 that delivers 382 horsepower to a twin-turbo V12 pumping out 604 hp, the S-Class offers a range of power plants that are sure to impress. Inside, the richly appointed cabin is adorned with high-quality leather and polished wood. High-tech accessories such as a hard-drive-based navigation system, adaptive seats, the Active Body Control (ABC) suspension technology and Distronic Plus cruise control offer an impressive range of capabilities that set the S-Class apart from the pack.

The 2009 Mercedes-Benz S-Class will no doubt satisfy just about any ultra-luxury-sedan buyer. But it's still worth taking a look at other options. Specifically, the all-new 2009 BMW 750i should be a more athletic-handling alternative to the S550, and the often-overlooked Audi A8 remains a favorite of ours due to its understated yet classy demeanor. And for those who can't decide between the two high-performance AMG models, the Bentley Continental Flying Spur sits nicely in between, both power- and price-wise. Still, Mercedes' S-Class essentially sets the standard here -- and that's something the world's celebrities, foreign dignitaries and well-to-do professionals will no doubt testify to.

Five trim levels are available on the 2009 Mercedes-Benz S-Class luxury sedan: the S550, the all-wheel-drive S550 4Matic, the V12-powered S600, the high-performance S63 AMG and the über-performance S65 AMG. Standard equipment on both S550 models includes 18-inch wheels, an automatic air spring suspension, bi-xenon headlights, an electronic trunk closer, heated and active ventilated front seats with 14-way power adjustments, leather upholstery, the COMAND control interface, a hard-drive-based navigation system, an in-dash memory-card reader, Bluetooth and a Harman Kardon surround-sound audio system with a six-CD changer and satellite radio. Optional on the S550 is the Premium 2 package that includes a rearview camera, a park distance system and keyless ignition and entry, as well as a sport package that includes 19-inch AMG wheels, dual-chrome exhaust and a body kit.

The S63 AMG, in addition to a larger, more powerful V8 engine, comes standard with all the features of the S550 and adds 20-inch lightweight AMG wheels, Mercedes' ABC adaptive suspension (optional on the rear-drive S550), larger brakes, park distance sensors, a rearview camera, specific exterior styling pieces, keyless ignition and entry and sport seats with massage function. An optional AMG performance package adds different 20-inch wheels and carbon-fiber trim, and the top speed of the car is raised from 155 mph to 186 mph.

The V12-equipped S600 comes standard with 18-inch wheels and all the features found on the S550, plus the Premium 2 package, the ABC suspension system, a panoramic sunroof, Night View Assist, the Distronic Plus system, heated and ventilated front and rear seats, four-zone climate control, dynamic-adjusting front seats with massage function, and power rear sun blinds. The S65 AMG includes all these features plus 20-inch wheels, dedicated AMG exterior and interior styling, special sport seats and a leather-trimmed sport steering wheel with aluminum shift paddles.

Many standard features found on the higher-end S-Class models are available as stand-alone options on models without these features as standard. In addition, a glovebox-mounted iPod integration kit is optional on all models.

The 2009 Mercedes-Benz S550 sports a 5.5-liter V8 that makes 382 hp and 391 pound-feet of torque. In testing, we've found that this is enough for a 6.1-second 0-60-mph time. A standard seven-speed automatic transmission routes power to the rear wheels. Opt for the S550 4Matic and this same transmission routes power to all four wheels. The Mercedes S63 AMG has a 6.2-liter V8 capable of 518 hp and 465 lb-ft of torque. The S63 also uses the seven-speed automatic, but it's recalibrated for faster, firmer shifts.

A choice of two 12-cylinder engines is found in the two remaining S-Class models. The S600's twin-turbo V12 is of the same displacement as the V8, but provides 510 hp and 612 lb-ft of torque. For the S65 AMG, a twin-turbo 6.0-liter V12 develops a positively ludicrous 604 hp and 738 lb-ft of torque. Anything more would have to be fueled by nuclear fission. Mercedes says the S65 AMG can hit 60 mph in 4.2 seconds. On the V12s, Mercedes sticks with a five-speed automatic since the seven-speed unit isn't capable of handling the V12's torque output. The S65 has a sport-tuned version of this automatic that provides quicker shifts.

Fuel economy is predictably mediocre for a heavy sedan with this much power. The S550 is rated at 14 mpg city/22 mpg highway and 17 mpg combined. The S550 4Matic comes in at 14/21/17 mpg. The S600, S63 AMG and S65 AMG all somewhat surprisingly achieve the same 11/17/13 mpg.

The 2009 Mercedes-Benz S-Class has some of the most advanced safety systems on the market today. Active headlights, stability control, eight airbags (including full-length curtain and side rear airbags) and brake assist are all standard, as well as Mercedes' PreSafe system, which can sense an impending crash and automatically tighten the seatbelts and reposition the power seats for maximum airbag protection. The optional Night Vision Assist uses infrared technology to detect objects far beyond headlight range.

Ride and handling on the 2009 Mercedes-Benz S-Class are compliant and fitting for a luxury sedan, yet the heavyweight four-door's capabilities go beyond what you'd expect. The Airmatic suspension system does a fine job gliding over bumps and ruts, and body lean is effectively minimized when the S-Class is equipped with the ABC system. The steering is fairly quick and precise with decent heft to the wheel, though we'd still give the BMW 7 Series a slight edge in road feel. Tight handling makes the car feel smaller than it is, even if we wouldn't exactly call the S-Class athletic.

Fit and finish is impeccable on Mercedes' flagship, and the materials quality is truly superb. When it comes to usability, many find Mercedes' COMAND system quirky and unintuitive, although the current generation of the interface is easier to use than in the past. Another pet peeve is the S-Class' turn signal stalk, which is located down lower than on most cars and is somewhat inconvenient to reach.

Optional dynamic multicontour seats have 11 air chambers that fill and deflate as you drive, which allows the seat to cradle your body in virtually any position. During aggressive driving, the side bolsters can automatically pump up and down in response to cornering forces to better hold you in place. These seats can also provide a soothing massage. Those in the rear seat can be taken care of in similar fashion, particularly when the S-Class is equipped with the rear-seat package that adds power adjustment, heating and cooled seats, and its own set of two-zone automatic climate controls.