The Mercedes-Benz M-Class SUV is just the right size and is set up well for many families. It isn't so large that it's cumbersome or hard to park, but it comfortably seats five and carries plenty of stuff. As daily transportation, it doesn't feel like a truck, and it won't beat its driver or passengers up. Yet it has the potential for some fairly serious off-road adventuring, and it can tow up to 7,200 pounds. The M-Class is more than powerful enough in any of its variations. And it offers the safety equipment, luxury accoutrements, style and smooth finish expected of a Mercedes-Benz.

For 2008, the M-Class line replaces the ML500 with the more powerful ML550. Also called the M-Class, the lineup continues to include the ML350 with its gasoline V6, the fuel-efficient ML320 CDI diesel, and the ultra-high performance ML63 AMG.

With the ML320 CDI, you can forget just about everything bad you knew about diesels. It's smooth and quiet, and clean. It gives up nothing to the standard, gasoline-powered ML350. It's equipped identically, except for its diesel engine. The 3.0-liter diesel V6 generates 398 pound-feet of torque, comparable to a large-displacement V8, and brings a substantial improvement in fuel economy.

The ML63 AMG features a hand-built V8 that generates 503 horsepower with AMG tuning and enhancements to match all that power. Though considerably more expensive than other M-Class models, the ML63 AMG is a true high-performance machine. Its 6.2-liter V8 is hand-built by a single technician. It bursts from 0 to 60 mph in 4.8 seconds, according to Mercedes, with top speed electronically limited at 155 mph. Plus, it comes with the full load of luxury features.

With increases of 80 horsepower and 55 lb-ft of torque, the new ML550 reaches 60 in 5.6 seconds, more than a second quicker than the previous ML500. It sports the same front end as the ML63 without all the amenities and super-sport equipment, and starts at roughly $30,000 less than an ML63.

The original M-Class helped make luxury SUVs a familiar part of the automotive landscape. Completely redesigned for the 2006 model year, this second-generation M-Class is better than the original in every way. It's roomier, more comfortable and more car-like in its bearing. Its wheelbase is almost four inches longer, and its body three inches wider, all to better accommodate larger Americans inside. In the bargain, the coefficient of drag, or Cd number, has dropped from brick-grade to a sylphlike 0.34, on par with many passenger cars that are much lower to the ground. This means quieter highway travel and better fuel economy.

In place of the original body-on-frame, truck-style design, this second-generation M-Class has welded unibody construction with isolated front and rear subframes, a technique that emphasizes rigidity, decreased vibration and lower weight. The unibody also reduces its overall height, making it easier for families to get in and out. The M-Class has given up any pretense to being a large-family vehicle. The optional side-facing rear seats from the old model are gone (they weren't very good anyway), so the M-Class is strictly a five-seater. You'll want to look at the GL-Class for seven-seat accommodations in a Mercedes SUV.

The second-generation M-Class introduced for 2006 brought a new look and larger size along with a double-wishbone front suspension and four-link independent rear suspension emphasizing sedan-style dynamics. Yet with a two-range transfer case on most models, and a sophisticated control program for the full-time all-wheel-drive, the M-Class can get its driver through some tricky off-road situations.

M-Class buyers will pay a premium over many other comparably equipped luxury SUVs, but those who appreciate the cache and engineering strengths of the Mercedes brand will find plenty to like here.

All 2008 models come standard with a sunroof, blue window tint and 19-inch wheels.