just FYI when I went to visit, I stopped by the Knoxville campus to take a peak of the outside: it's a larger building than the Harrogate one (at least it spans further horizontally), it's on the side of a freeway, and it's in a business park... in my opinion, not exactly what you'd envision a traditional medical school to look like.
From my visit to both campuses, the downtown area in Knoxville, and my emails with the admission staff, this is what I think -- take it w a grain of salt though because nobody knows anything about how Knoxville will work just yet:
If you are a little more of a loner and prefer to study/learn/live/adult independently, it seems like the Knoxville campus is better. There are fewer amenities (l don't think they have a student gym, no student housing, etc.) but downtown Knoxville is sooo cute, only ~15 minutes a way (by car), and I can imagine that I would frequent the cafes to study. Also if you want to have better food/nightlife options, Knoxville may be the choice because you have all of the city to explore. Like I said, if you are someone who maybe makes 1 or 2 really good friends and prefers not to get involved in large social functions, this may be a better fit?
However, Harrogate campus has more established social functions (student clubs, gym, student dining/housing, etc.) and you may have more access to resources directly supplied by the school itself... I think I'd equate it to the same resources you have as an undergrad living on a college campus. If you need to go in to lab to practice/study or need to talk to a professor, just walk up a hill and you're there! However, there (seems to be) literally nothing outside of Harrogate -- this may be a turn-off if you come from a city/diverse area. All there is to eat is fast-food, and even that is few and far between.