I concur with San Francisco. I don't know where you are flying from but San Francisco has excellent public transit, the weather will be decent, and there is so much to do.

Another place we tend to go (no car rental required) is San Diego. Santa Barbara is nice but only regional aircraft fly in there and the town is a bit away from the airport. It isn't a bad cab drive though.

This sounds like a great trip! I'll keep checking this thread to see if you have questions. While I don't know as much as some of the people who live in the cities, I travel a LOT and feel the same as you about being stuck in traffic. I try never to rent a car if I can help it.