It's a close call. I agree with the Ninja - where do you want to live? Bloomington is in the north, has basketball, lots of arts and lots of hippies and activists. Athens is in the south, has massive football (could be national champs this coming season), and less arts, more sports/sports culture.
Both at one time or another have been anointed as a "party school" by Playboy or the Princeton Review. Both have bars where Playboy regularly visits.
Athens will still be steaming hot in August when school starts. Bloomington will be less so. However, Athens shuts down at the slightest hint of snow. Bloomington would require a blizzard before classes were canceled.
Both are near lakes with boating/fishing opportunities. Bloomington does have the advantage in foliage, though - it's in the middle of a band of deciduous forest that turns technicolor every fall.
Both are an hour or so from larger cities with more to do (Indianapolis and Atlanta). I've been to both towns. I went to school in Bloomington, and had family in Athens. Have you visited? And is there anything else you'd want out of school that would tilt you either way? For example, UGA also has an urban planning and urban landscaping department, IU does not. IU does, however, have a better business school and a school of environmental and public affairs.