The Mercedes M-Class was one of the first premium SUV models, and it set the template for rivals such as the BMW X5 and Porsche Cayenne. Now in its third generation, the latest M-Class is the biggest and most refined yet, while the recent addition of a four-cylinder diesel version makes it one of the most affordable to run. Unlike its sporty BMW and Porsche rivals, the Mercedes has been designed with comfort and refinement in mind. As a result, wind and road noise are well surpressed, while the interior is one of the biggest in the business - although there's no seven-seat option. The engine line-up includes a pair of punchy and frugal diesels, plus a muscular twin turbo 5.5-litre V8 for the firebreathing ML63 AMG version.

The Mercedes M-Class is available with a 3.0-litre V6 diesel in the 350 CDI or an entry-level 2.1-litre four-cylinder diesel in the 250 CDI. The latter is surprsingly punchy thanks to its muscular 500Nm torque output, and can sprint from 0-62mph in a claimed 9.0 seconds. But for the ultimate in refinement and relaxed driving the V6 is the one to go far. Both versions use a smooth and responsive seven speed automatic gearbox. Refinement is good, as wind and road noise are well surpressed, as is any racket from the engine, even in the four-cylinder diesel. However, ride comfort is an issue, particularly at low speeds where the car crashes into pothholes. The ML350 CDI is availble with the supple air suspension upgrade, which is well worth the extra expense. For the ultimate SUV driving experience, then look no furher than the ML63 AMG. Not only will it rocket from 0-62mph in just 4.8 seconds, its uprated uprated suspension, sharper steering an torque vectoring kit result in surprisingly agile handling. All versions get permanent four-wheel drive, while 350 CDI models are fitted with an off-road button that tunes the traction control for slippery conditions. Even so, the M-Class isn't as capable off road as a Range Rover Sport or Volkswagen Touareg.

A big four-wheel drive off-roader should cost the earth to run, but Mercedes has done a great job of ensuring that's not exactly the case. The 2.1-litre four-cylinder diesel claims 44.8mpg and emits just 158gkm of CO2 when riding on standard 19-inch alloys. Even the V6 model promises to return 39.2mpg while emitting a respectably low 179g/km of CO2. Of course, the ML63 is much less efficient, but buyers of this sort of car are hardly going to lose sleep over a shocking 23.9mpg combined fuel figure. However, while the everyday running costs of the diesel are reasonable, you can expect hefty bills for insurance and maintenance. And like all Mercedes models, it's easy to get carried away on the expensive options list. Still, at least you won't lose too much cash when its time to sell, as our experts predict the M-Class will hold onto an impressive 60 percent of its value after three years.

Sharply creased bodywork and elegant LED headlights help the Mercedes M-Class stand out. However, it's not perfect, as the slab sides make the car look a little ungainly and top heavy in profile. There are two trim levels to choose from - SE and AMG Sport - with both benefitting from 19-inch alloy wheels and bold LED daytime running lights, while the latter adds an aggressive body kit. Spotting the range-topping ML63 AMG is easy thanks to its 20-inch alloys, wider front wings and bonnet that features an aggressive pair of air vents. The cabin follows the familar Mercedes template of conservative design and high quality materials. Fit and finish is excellent, while the quirky single stalk control for both the wipers and indicators becomes second nature after a few miles behind the wheel. There's also a decent haul of standard kit, with all versions getting sat-nav, climate control and Bluetooth connection. However, the SE and AMG Sport get Mecedes' Artico artificial leather trim for the seats - real leather is an extra cost option.

The huge exterior dimensions of the M-Class mean space in the cabin won’t be a problem, with huge amounts of room in the back seats for even the tallest of adults. The driver and passenger also get a wide range of seat adjustment, while the car's high riding stance gives a commanding view of the road. The boot can swallow 690 litres of luggage with the rear seats up, or 2,010 litres with them down. There's also a host of handy hooks and storage trays to keep things from moving around, plus a handy 12V power socket. Better still, AMG Sport versions benefit from a standard powered tailgate, which takes the strain out of loading up when you've got your hands full with shopping. Mercedes doesn't currently offer a third row of seats so larger families will have to look elsewhere.

Mercedes has pioneered many important safety technologies throughout the years so each of its cars is destined to be incredibly safe. The new M-Class is fitted with Pre-Safe to help minimise collision damage as well as ESP, ABS and a whole host of airbags. Optional systems like automatic braking, lane-keep assist and blind spot assist will all help keep you out of trouble. The new M-Class is too new to assess its reliability but its rare for a new Mercedes to prove unreliable, while the brand finished in an excellent fifth place in our 2013 Driver Power customer satisfaction survey.