LA- I spent two weeks in Venice Beach weeks a few years ago which was fun but a bit dodgy at night. I'd stay in Santa Monica which is next door to Venice, some great bars etc in SM and its pretty safe to go out on the lash. Its also easy to drive around LA from SM because of the easy grid road system. Just do all the usual tourist sights, Hollywood Boulevard, Rodeo drive etc also you have to go to Universal Studios, much better than the Florida one and that takes some doing. Also some good nightlife around Hollywood boulevard but its a bit more spread out and you need to get taxis to specific clubs etc. I'd do that in SM all in one place. Avoid downtown its a bit ghetto and not especially safe.
Santa Barbara and Carmel are supposed to be really nice, kicked myself for not going but everyone told me how nice they were.
San Fran- I stayed here for about $80 for a double private room if I remember correctly, decent location and sensible price for SF
http://www.sfhostels.com/downtown/features/Tons of stuff to do around the city, See Golden Gate (if its not foggy lol) and golden gate park, go up to Coit Tower, good view of GG bridge, the bay and part of the city from there. Lots of restaurants and bars at Fishermans wharf, and you can get the ferry to Alcatraz from here. There is lots of nice areas to the city just walk around or get the cable cars which are good fun. The nightlife is a bit hit and miss in SF and spread out. Go to Vesuvio bar in North Beach (Italian district) its very nice and there are quite a few bars in the immediate area and some some decent italian eateries.
Have fun
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