I grew up in the San Diego area, so that would be my vote. The San Diego Zoo is one of the finest in the world, and you can easily spend a couple of days there. There’s a Sea World, too, which is fascinating. Balboa Park is huge, and has tons of different and interesting activities going on all the time. The last time we visited, we ate our way through Seaport Village (I think that’s the right name) a couple of times. For sight-seeing check out the landmark Hotel del Coronado (where the movie "Some Like It Hot’ was filmed), and plan a day trip to Mount Palomar Observatory with its 200-inch-mirror telescope, or visit Point Loma and the Cabrillo Lighthouse, San Diego’s Old Town – the list goes on and on. It’s a fairly easy daytrip to Disneyland from there, too.
I loved San Diego then and I still do.