Just moved back to SoCal after living 5 years in the Bay Area. So I can speak pretty well on the topic.
It depends on what you're looking for, but I'll try to break down some of the key factors:
Job/Profession - NorCal pays better (I'd say 10-15% more than Socal), but the work life balance is usually worse. People work harder in the Bay Area, and they import really smart people. There are really smart people in SoCal, but everybody in the Bay Area is either really smart or works really hard.. Tech rules in Bay Area, LA has entertainment if that's what you're looking for.
Cost of Living - NorCal is ridiculously more expensive than LA. It's hard to find a 2bedroom condo in South Bay/Peninsula/SF for under a $1M. LA has really expensive areas (Santa Monica), but they also have a ton of more affordable places. The Commute in LA is as awful as you've heard of, but Bay Area is slowly catching up. Expect to pay ~$3000 for a 1br in SF, $2000-$2500 Peninsula, $2000 East Bay/San Jose. In LA, Santa Monica $2500+, rest of LA $1000-$2000
Activities - I'd call this close to a tie. Bay Area has a bit more hiking and outdoors stuff, LA has more fun stuff to do. Beaches in LA are much better, Tahoe is further but better than Big Bear, Bay Area has better hiking
Women - LA by KO, Bay Area can't even contend. They call women in SF 49'rs, 4's that act like 9's. SF is pretty balanced ratio wise, but outside SF it's a giant sausage fest. LA women are hotter and in general better shape (A good chunk of women do Yoga/Pilates/Spin in LA). On the surface LA girls are more materialistic, but girls in SF expect you to be on a career path or working for a hot new startup
Nightlife - LA wins by a pretty heavy margin. SF is no nightlife wasteland, but few places top LA
Food - LA wins by a slight margin. SF has fine dining in Napa/Yountville and some decent European food overall, but LA wins by it's massive selection of ethnic food. For Asian food for example, SF has decent Asian food, but LA has much more competition and heavily centralized ethnic areas (notable exception is Indian food, and Viet is a tie)
Getting Around - FYI you need a car in LA. The metro is getting better, but SF has Caltrain and Bart. I'd still recommend a car in SF, but you can get by without one espcially if you live in SF
Let me know if you have any questions.