Car is a liability is SF. Save your money and take BART from the airport. If you don't have kids, stay at the Holiday Inn in Civic Center. The central location is not great for hanging out, but it is a great launch point to reach key areas of SF. Also, SF Bay Area has the second most expensive hotel rooms in the U.S. after New York City...and Fisherman's Warf has the highest prices on the west coast...so I would avoid the Warf. You can take the trolly to Fisherman's Warf...it's a great ride. after dealing with the Warf, you can go to Union Square, SOMA and North Beach for the nightlife.
This is the peak of the travel season, so your hotel rates will be higher than normal...