LA is ****ing awesome. I flew into LA, drove to San Fran, then to Las Vegas, San Diego, El Paso then back to LA. If you want a mashup and you're over 21 then Vegas is the place to go dude. Its insane. LA is pretty awesome to go out in as well although I only went to a house party with a bunch of rich kids but they told me the scene is pretty wild. Depends what you're into I'm sure you'll find something....If you're into scenic then recommend the drive from LA to San Fran on route 1 its pretty cool. Rent a mustang and do the drive. San Fran is alot less party party I went to more ****tail bars it was a bit more mature.
One word of warning...your british accent will get you alot of tail if you go to the right place haha trust me you wont barely have to try. unless your really ****ing ugly..in which case go Spain :P