If you work at it a little, you can demo bikes for free. Catch a shop when a demo fleet is visiting, or try a demo day - although demo days are known to have ridiculously long waits for the most popular models in the most popular sizes. Get a good relationship with a shop, and you will likely get to demo a few bikes for one fee. The whole "applied to purchase" thing is OK, but once you've paid to demo two bikes that didn't impress you and you decide to try another brand at another shop, you kinda wish you had your $150 back.
@Davide a Transition Scout or Patrol would be a great bike for SoCal terrain, IMO. But there's a lot of different SoCal terrain - lots of long boring fireroads, many steep loose trails, lots of rocky, chunky, steep runs, several moderately pitched singletracks with fun little drops or berms, etc. The question is more, what trails and what speed do you like to ride? Are you a climber who tolerates descents, or a descender who tolerates climbs? Are you an all-day epic with long miles guy, or a quick spin 10 miler dude? Steep gnar? Bike parks? Whaddya like?
For many guys on this forum, a hardtail singlespeed is the right bike for SoCal. For those with more sense, it's a 5-6" travel trailbike that brings them to their own SoCal Nirvana. Get what floats your boat and makes you smile and want to ride when you look at it.