Another vote for "must have a car". You can easily get to Santa Monica on The Big Blue Bus but I think after that you're relatively stuck. I'd also agree with a GPS if you're not familiar with the areas you're going to.
I have liked Santa Monica it's relatively central I think plus it's a tourist requirement to walk down to Venice beach and gawk at the life there.
I've been down in Orange County a few times with work this Fall and have liked it too. One of my coworkers lives in Hermosa and likes it. We stay in Costa Mesa or down in Laguna where a couple of the guys live (Laguna is really sleepy). Typically ended up in Newport Beach for a night or two. It seems to be a rather young crowd...
__________________
|