Get metric tools for sure. Most of the nuts and bolts you're likely to handle will be covered by a set that includes 8, 10, 11, 12, 13, 15, 17 and 19. A set of standard sockets, deep sockets, open wrenches, combination wrenches (open on one end, box on the other) should be plenty. get the sockets in both 3/8" and 1/2" drive to the extent that they're available.
To drive the sockets you'll want a rachet handle and breaker bar handle as well as an assortment of extensions. My u-joints don't get much use. I much preffer wobble extensions. And a torque wrench, of course. I find the 'click' type easier to use than the beam type (needle on a scale). Most MB specs are provided in Nm so make sure it has that scale or a dual scale (with lb-ft).
Depending you what engine you have, get a socket to turn the crank. I think 27mm is what most MBs use. Only a really big tool set will have a socket this big.
I'm not mentioning generic tools like screwdrivers and pliers.
I'm sure there are a lot more tools you'll find useful based on what you do and how you like to work. A tool set is a good place to start, then buy the other pieces you need as necessary.