Which Model Mercedes Are the Most Reliable?

I am looking to by a older Mercedes (late 80s early 90s) (the square headlights) but I have a few requirements such as not going slow as balls (although I know its a Mercedes, not a race car) but i also don't want a V8 I'm looking to get above 20 mpg and the biggest necessity (which would out weigh the rest) would be reliability, I heard certain Mercedes are solid just wondering which ones.

Suggestion:

From that era, the W201 (190E), W124 (300E) and W126 (300SE) are all generally quite reliable vehicles. Just keep in mind though that you are dealing vehicles around 20 years old so how they have been driven and maintained over the years will need to be a big consideration.
The diesels usually do better as far being more economical and robust but they are a little slower compared to the gasoline versions. If you are looking for economical but not "slow as balls", I would recommend the 93-95 300E/E320 (it was called the 300E in 1993). This E-class came with the M104 inline 6-24 valve gasoline engine and it moves the car pretty quickly. Up to 1992, the E-Class sedan came with the older M103 engine which was a 12-valve inline 6 (but note that the E-Class coupe with with the newer M104 engine starting in 1990). The 24-valve version really wakes up the car compared to the 12-valve engine.