Personally, I would go for the 15'' MacBook Pro. I am going to college next year too, and I'm getting a new MBP with a hi-res screen in a couple of weeks. The 15'' is nicer than the 13'' because you can have 2 windows open next to each other, which is very nice when writing a paper and doing research online simultaneously. With the 13'', the screen isn't wide enough to see 2 windows next to each other very well.
Also, I don't know if other colleges have this, but at the University of Minnesota bookstore, you can get free AppleCare when you buy a new MBP in addition to the significant discount you already get when buying for education.