This is a little hard for me to respond to, because I grew up in So. Cal, so I go back there far more often than I go to WDW. If I were going for Disney and Disney only, I'd probably pick WDW. But DL has things WDW doesn't. Most of CA isn't at WDW. California Screamin' is an
awesome roller coaster! Plus, So. Cal. has so much more to offer than just DL. There's the beach, San Diego, Hollywood, the beach, Catalina Island, the Queen Mary, oh, and did I mention the beach?
You'd need to rent a car to get to these places if you're staying at DL, (and some are a bit of a drive) but it can be a great vacation, it's just not all Disney all the time (IMO). If you want more theme parks, there are also (like Orlando) Sea World and Universal Studios, and (unlike Orlando)
Legoland (which is a fabulous park for kids!), Magic Mountain (tons of great coasters) and Knott's Berry Farm (which doesn't hold a candle to DL, I'm surprised someone picked it over DL, but hey, it's different, if you think you don't want another day at DL, I guess.)
Anyway, that's how I see it. If you want nothing but Disney for a full week, WDW is the better choice. If you want 2/3 days of Disney, plus some of the other things I listed (and thensome -- check some travel sites to see what else), give DL a try.
Oh, and I almost forgot about the time of year. In the midst of summer, I'd choose DL for sure. It's not nearly as humid in California. Personally, I don't think I'd ever go to WDW in the summer.
And another thing! It seems like when I read threads like this on this board, people who first visited WDW don't like the fact that DL/CA are in the middle of the city. They don't like being able to see streets, buildings, etc when they're in DL. Funny thing is that for me, growing up going to DL often, I never noticed any of that. I didn't notice a difference going to WDW second, but some people seem to notice a difference going to DL second. Just more food for thought.
Good luck. Either way, you'll have a great vacation.