Guys, maybe I'm biased, but to me South Florida, and more specifically, Miami is paradise. There is great diving all the way from Jupiter (West Palm Beach area) in the North, to the Keys in the South. (that's not even mentioning the fresh water springs/cave diving in Central Fla, and the diving on the Gulf side!) Though I've never dove in California, I did go to Santa Monica in AUGUST and I couldn't even put one foot in the water it was so cold...not for me. I have a couple a friends that live and dive in Cali and they don't seem to be to impressed...but who am I to say?
As far a Florida goes:
Jupiter has some good drift diving and great spearfishing.
Ft Lauderdale has good beach dives and wrecks.
There are quite a few wrecks in Miami, they have this thing called the "Wreck Trek" which is a mapped out series of wrecks all along the Miami Beach coastline.
Then, of course, you have the keys. Key Largo alone boasts enough diving to keep anyone occupied for years. Fantastic reefs, and marine life, great spearfishing, and also some really great wrecks.
There are the Coast Guard sister ships the Duane and the Bibb. Both are wonderful dives (the Bibb in on her side) and then there is the grandmama of them all: The Spiegel Grove, a 510ft Navy Ship that was sunk a couple of years ago and is the largest ship to be sunk as an artificial reef/dive site (until they sink the aircraft carrier in Northern Florida next year!!)
I dive the Spiegel 2 or 3 times a month when the weather permits. It is so massive that it's impossible to see the whole thing in one dive. There is great penetration available, some are already roped out for your convenience and safety. She lies on her side and starts out at around 55ft at the middle of the ship, and descends all the way down to 134ft. We never get tired of it.
The water temp is mid 80's in the Spring/Summer/Fall, and Mid 70's in the winter, so you don't even need a wetsuit in the summer and can get away with a 3mm in the winter...in Cali I believe you need a 5-7mm in the summer and a dry suit in the winter!!!
I've been to Turks and Caicos, and Cozumel so I think I can comfortably say that the Florida Keys are a wonderful dive destination, not just in the US, and an awesome place to live.
I could go on and on...but I'd hate to bore you!!!
That's my 2 cents (more like 4 cents)
