I think a lot would depend on the records and history on each car - they all have something to offer. The 123 300D is supposed to be nearly indestructable, but heading onto 20 years old some of the rubber and plastic may be getting a bit stiff and brittle. The 190 is a 5 speed, which I like, and probably gets better gas mileage and is newer, but is smaller than the other cars. The 124 bodies are very solid and supposed to give high survivability in accidents, but get less mileage than the others for the gas model (about 22-23 hiway on my 87). That said, diesel fuel is more expensive than premium out here (1.99/gal), which kind of offsets some of the economy advantage over the gas.
I guess it depends on what you are looking for. Economy, safety, size, reliability, ease of freeway driving (rules out the 5 speed during rush hour out here - smell that clutch cooking!). They all sound pretty good, so choose the best condition, records and repair history that fits your needs.
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E