As a fellow college student (I was a freshman this last year) I would definitely say to get something in the 13'' range. 15'' laptops are great, but for all the moving around you do I think 15'' is too big for a college student. This last year I had a 15'' MBP, but I only had that used as a desktop as I also have an 11'' Air, which is absolutely perfect for a college student. Personally, I don't see much use for iPads at all in a college environment. I feel like many of the people that use them in college simply use them because they have one. Certain things are useful on iPads, but it's not really a productivity device and that's what you're looking for as a college student.
Instead of a Pro, I would highly recommend a 13'' Air. There is something about the Air, and many will agree with me on this, that is intangible and makes it fun and great to use. The light weight and thin frame make it a more enjoyable, portable laptop to use. Also, SSD's are damn amazing and HDD's will only cause you problems. If you really feel you need a disc drive, get a Superdrive, but really think about how often you use a disk drive. Many people will say the Air is underpowered, but unless you plan on doing hardcore gaming or something extremely intensive, which 99% of college students don't, the Air will be more than powerful enough for your tasks everyday. However, if you're set on a MBP, I'd get the 13'' with 8GB of RAM.
This is all my opinion, but me being a college student as well as significant time spent with all of these laptops helps 🙂