Tough to answer...it's hard for someone else to know what you're looking for. Somewhat depends on can you work on cars even a little yourself or do you go to the shop for even an oil change? Economic situation...real job, crummy job, student, family... Got any tools? (Yeah I know P.E.H. it's pose'd to be "do you have" but it's a car/fun forum not a job application.) Sorry I got sidetracked...
Anyway the dsl's are very reliable cars(I know squat about MB gasos) but no matter what 123 you get it'll be 20+ years old and will have at least minor issues. No one sells a great running car in great shape that gets 30 mpgs, paid for etc so it'll need "something". Any used car/truck I buy I expect to and usually do put $500 in right off the bat. Tires, clutch, suspension or something... Did I mention a 20+ year old car gaso or dsl will need something or it wouldn't be getting sold(ok, there are RARE exceptions).
The early 123 dsl's are easy to work on, parts are reasonable and easy to get and if you have a good 123 to start with are very reliable. Again I know zip about the gaso MB's and can't comment.
Give us a bit bit more info about you. If wrenching isn't new to you 123 dls's are easy. If wrenching is a foreign concept the 123 dsl's are a great place to learn. If you don't want to mess with getting greasy at all and go to shop for everything I'd stay away form any 20-25 year old car. Good luck.