Either is fine, do your programs need Windows or MAC or can run on both? You can really just pick them based on price if the operating system does not matter to you.
I would never pick a MAC over a Windows system myself, but that depends on the programs you run and what they run best on, as well as everything else you and the school use. If you have iPhones at home, and many people use a MAC at school, that may be the way to go.