As a student who is currently in college, I went for the Air. I'm a commuter and my shoulder and back thank me for the lighter but relatively powerful system. Even between classes, unless you are used to holding heavy books in your backpack get the Air your back will thank you for it later.
As far as future proofing it, I have the i7 13" version, and it certainly is the fastest computer I've ever used. The 4GB memory has never been a problem with me as I usually have many applications open at once. (Everything from Audio editing to word processing)
Computers these days aren't getting exponentially faster anymore, so it is likely the laptops will start to last longer as this trend grows. More cores don't mean anything if the software can't take advantage of them, and many applications these days still don't and it will be a while before they start to take full advantage of multicore systems. Today, it seems the trend is more toward efficient software as opposed to faster hardware (for the PC world anyway). I have an old HP laptop that I got 5 years ago, and it still works great for word processing and photoshopping. The only issue with the Air is the lack of a CD drive which I found I needed to use once for work, I bought a relatively inexpensive external DVD drive for it, so that is no longer a problem, but if connectivity is something that is important for you, then the Pro would be a better choice.
The choice here would be connectivity and expandability. If your college doesn't have wifi (which I highly doubt), and there are little to no computers on your campus, then go with the Pro. The computers on campus would be those rare occasions you may need to use a connected printer or something.
Do you have a lot of files that you need to be able to access immediately, like music, movies, photos? If so, get the Pro. So if these two points are important to you, a Pro will better serve you than an Air. The Air is certainly capable of these, but carrying dongles around isn't the greatest thing in the world. Like my external DVD drive, and my Ethernet Dongle, still I rarely carry them.
Either way both computers will last 4 years. I wish you luck on making your decision.