I was in Las Vegas for a few days last month (my 4th time there) and I personally hate it.
Granted, I've never been off the strip, I don't gamble, and I never go to shows, so your mileage may vary. I was there for three days before I moved to DC, and I easily blew $800 on food and drinks (I am a bit of a drinker). One steak dinner for my date and I with two bottles of wine ran just over $200 with tip. I've heard it's cheap if you're gambling, as casinos tend to comp things, but I imagine your gambling losses more than makeup the difference.
San Diego is probably one of my favorite places in the world. Great food, AMAZING weather, beautiful scenery everywhere you look, the people are generally friendly and helpful. I taught at UCSD for a summer, and I've been there maybe 8 times outside of that, so I feel like I've got a pretty good hold on the town and it's outlying areas. There's something for everyone.
I spent a lot of time in LA as well, and find it to be generally depressing, although somewhat entertaining if you can take pleasure in the desperation and dillusion of others. Lot's of trashy folk and failed/failing actors. It's the type of place that really makes you appreciate what you've got. While you're there, take a studio tour of Warner Brothers or Paramount. Those are pretty entertaining and very informative. If you don't mind waiting in line for a few hours, see if you can get tickets to The Jay Leno show, Carson Daley, or Jimmy Kimmel Live. Those are a lot of fun.