All the coastal cities are nice, and safe. Pretty much nothing but rich white people living there though.
So where can i find Black , White , Asian and Hispanics living together at ?
West L.A. i.e. Santa Monica, Venice, etc. All neighboring cities to that of UCLA (No surprise, it's the #1 school in terms of amount of application it gets each year).
As for L.A. vs SD. I'd give the nod to L.A. because L.A.offers more to do than SD. If you want to try out different bars/lounges, etc.. there's always downtown, hollywood, pasadena, PCH, santa monica, etc. Same goes with food.. go straight to little mexico (huntington park/East Los), asian food (SGV), etc. There's always some event popping every week whether it be a festival, art exhibit, dj spinning, etc. Traffic sucks ass though but if you're someone like me who tends to get bored and needs to keep moving then L.A. is the place for you. I love SD, much more chiller, cleaner, etc.. but it doesn't offer the options/choices that L.A. does.