I'd consider a 4-cylinder or diesel W201, or, if you can afford it, think about a non-supercharged 4-cyl W202. While the W124 is a nice driver, the gas mileage on a 300E at least isn't anything to write home about. I think you could eat up a lot of cash with gas costs. I don't know much about the 190s, but the early C220/C230's get surprisingly good hwy mileage (low to mid 30s) depending on your driving style. I just did a 1000-mile round trip in a '00 C230k and it gave me 28-30 mpg while cruising at 80+, I'd imagine it'd be a couple/few mpg higher at more reasonable speeds.

Either way, try to figure a total-ownership cost for the number of years you'll be commuting to school in your purchase decision.