I am taking college courses online and my college requires a Mac and it will also be useful to be able to use every operating system legally. I was just wondering which I should get. I won't be moving around but I have a 27" 1080p monitor and plan to eventually get another monitor at 1440p for my birthday. I'm just debating which I should do.
It depends on your workload. If you just need to be able to boot into any operating system for general purposes, consider either a Mac Mini or Dell Workstation (refurbished on both counts). For about $350 you can get a Dell Precision T3500 online (I like the Precision line from personal experience) with a Quad-Core Nehalem Xeon and up to 24GB RAM. Install Windows XP, Vista, 7, 8, and any flavor of Linux you can think of with reckless abandon in a robust, upgradeable system and on the relative cheap.
With the rest of the money, a base-model Retina MacBook Pro (refurbished!) is an excellent machine. Then again, so is a maxed-out MacBook Air. I have a rMBP for work and my personal laptop is an 11" MBA, and both are amazing for different reasons. But for college, no matter how immobile you project your schedule, you'll want a laptop at some point.