what degree are you taking for college? i say it would depend on that.
Im taking up Electronics engineering and im using an ipad 3 for my textbooks and pdfs, especially for powerpoint and word
i had a macbook pro but i sold it to use a windows computer. All my engineering simulation programs run on windows(Pspice,electric,matlab,isis,hitech and iAR)
For everything else like business or design
Sell both,
Get a rMBP and an ipad 4 or 5 when it comes out.
nothing beats retina display! the full size ipad will really be easier on the eyes for reading.