As someone who has taken semesters at both schools (full disclosure- i'm an ole miss alum though), I thought the two cities couldn't be more different.
What always stuck out to me, though, was that you can walk around places in Oxford. There's the square, the neighborhoods around it are full of cool people who like to party, etc. There's not really anywhere in Starkville that has nearly as much stuff in one centralized location. If all of Starkville's bars were on that downtown strip, that'd kick ***, but they're not, they're spread out all over the place. The walking thing is huge, because if I can walk from a friend's house to the square and back, I go out alot. If I always have to drive, eh, I'll still go out, but it's not the same.
Cities with dense districts always have a cooler vibe. The Square in Oxford is an example, The Strip in Stillwater, OK is an example, even Cooper-Young in Memphis is a good example. Starkville just completely lacks that.