Hard to compare them as they are completley different cars.
Pro's for EK: Hudge aftermarket, more performance oriented and i think the engine/box combo is far better.
Cons: Expensive for what they are unless you find a high milage molested example.
Pro's for MB: Dirt cheap for the ammount of car u get. Good spec, reliable engine, plenty of space, comfortable and awsome stereo lol!
Con's: virtually no aftermarket, crap gearing, crap suspension, horrible dash and living with the rover/mg heratige.
Basically it all boils down to what you want from a car and choosig accordingly.