I will take Austin over Athens 100 times out of 100 from a "Best college town in America" POV.
I've been to both. But why? Because Austin has more population? Because they have a bunch of bats under a bridge? South by Southwest? I'm not saying you're wrong, and I'd probably be in Austin too. But it's not as compelling as you make it out to be.
I have been to both and would certainly live in both cities. Obviously, if you forced me to live in either city I would be a happy camper, but if it came down to personal preference I would select Austin. It's like asking which is better; pie or cake? You can't beat either, but it depends on the person.