In general, I would say Oakland is the best bet, followed by San Francisco. San Jose airport works fine (about 1 hour from Berkeley with moderate traffic), as long as you're not doing it during rush hour. However, if you are flying out of Nashville, you can often get good prices on tickets to either Oakland or San Jose (try Southwest and United). Also, Sacramento will work, with probably a 1.5-2 hour drive to Berkeley. If you are wanting to go to the Sierra Nevada (i.e. Tahoe and region), then Sacramento would be ideal as it is between Berkeley and Tahoe. I have regularly flown out of all of these airports (Oakland, San Francisco, San Jose, Sacramento) going to Knoxville and back and they all work fine. It's just a matter of whether you mind a bit of a drive. If so, Oakland and San Francisco are the closest to Berkeley.