Living in Northern California in the San Francisco Bay Area, we already have "perfect weather" so I'd definitely choose never to be stuck in traffic. It's horrendous commuting to SF everyday. What should be a 25-30 minute drive usually becomes an 1 1/2 - 2 hour drive everyday.
I would definitely choose to go back and change something. I would love to go back and study harder, take school more seriously., go to college and have a "real career" rather than just working at "jobs" for 51 years.