Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Depends on what you are going to do. If you are just writing papers, any model will do, and I'd suggest you even save and pick up a refurb / '09 model for that work.

If you are going to get into graphic design, multimedia editing, CAD, or business/game development - you'll almost certainly want an external monitor regardless.

So I'd suggest either a 13 or 15" - with a 24" External monitor for when you are doing your "serious" work. :) I do development on both my 2010 13" and my 2008 15" - but when I have a lot of editing or spend significant time in Xcode, I'm always using my 22" or 24" in combination with my MBP screen.
 
i was going to buy the 15" with the hi-res screen. I could easily afford the $700 premium over the $1099 13", but went with the $1099 13 incher today. two reasons:

15" was too heavy and didn't fit in my bag
For $900 more, I could just buy the LED display if I really wanted it and solved the higher res screen problem.
 
I'd head for the 15" if it will be your only machine. You'll benefit from the dedicated video card, bigger screen, vastly better processor.

SSDs are great, but they are still very expensive and if you can make do, a 7200RPM drive should be fast enough. Possibly consider the new Seagate Momentus XT.

Good luck.

Consider the MBA with the SSD ... it's noticeably LIGHTER than the MBP.

Except that would mean spending more money than the base 15" and having lower specifications (at least the parts you can't upgrade).
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.