Is this your only motor vehicle? Are you a DIYer (do it yourself)? Where do you live and how fasr is your search able to extend?

I'd say for starters, no older that mid 90's. Gas or Diesel, as MS asked?
Mid 90's W124 coupe (300CE/E320) might be a good place to start (and maybe finish). If you are really interested in sporty, consider a W124 convertible. I pretty much am saying what Tyler has posted. The M103 and M104 L6 engines are strong and durable. Like anything else they all have their quirks.

http://www.peachparts.com/300e.htm

I don't own a V6 or V8, but the bigger the engine, the greater the complexity and the broader the problems as a general rule. Some late 90's models had serious build (rust) and mechanical problems, with things like harmonic balancers

Buy nothing without a history check (Carfax) and an independent inspection at a dealer of your choosing.

Happy Motoring!