Is there a reason why you can't fly right into San Diego? Clearly that would be the easiest. Long Beach is located closer to San Diego than LAX is, but it is a small airport. LAX will have more chance of lower fares (more carriers, more flights).
Long beach, but LAX will probably be cheaper. I agree, just fly into San Diego. It will save you a lot of time and probably money over Long Beach as well.
I agree with theluckyrabbit flying directly to San Diego makes more sense. LGB is still really close to Anaheim as is SNA. LAX would be the farthest. I guess it also matters where you are flying from.