Well, I just got back from La Paz about three weeks ago and the diving is much much better than Cabo (I dove Cabo three years ago) in my opinion. The water in La Paz is also warmer. There are only a few sites in the Cabo area and they are about a 5-10 min boat ride from the shore. The life is decent with lots of fish, a few sea lions, a few regular white tips in the area, and some pretty cool rock formations. La Paz has many more sites (for those doing multi-day trips), TONS of life, sea lions, whale sharks, hammerheads (although we never saw any...lol), and the boat ride outs are like watching a discovery documentary (rays jumping out of the water, huge pods of dolphins, we even saw two blue whales!). Also, in between Cabo and La Paz is a place called Cabo Pulmo and the diving there is very nice also. I know you can sign up for a day trip to Cabo Pulmo from any of the dive shops in Cabo.
Good luck and let me know if you have more specific questions.