I haven't done any land based diving from La Paz, but I've been on 2 trips on the Don Jose with Baja Expeditions out of La Paz.
I found the diving to be incredible in October, with huge schools of fish and schooling Hammerheads at El Bajo, as well as literally dozens of morays; more hammerheads and other critters at Las Animas; and playing and interacting with 3 juvenile sea lions for nearly 2 hours, on an 18 foot max depth dive at Los Islotes on the northeast side of the island.
The trip we did in April, the diving was not as good because visibility was pretty bad, but that was expected. That is the time of year when the plankton are heaviest. We saw and swam with 5 whale sharks that week, saw a mother fin whale and calf, saw mantas, mobilus rays, dolphins galore, got in the water with a mixed pod of dolphins and pilot whales, and yes, more sea lions. I did manage to get a nasty burn from a Portuguese man 'o war on one dive.
There is more large marine life in the Bahia de La Paz and that general region than I've ever seen anywhere in the Caribbean. Just don't expect to see much coral, or lots of little reef fishes because it is a very different environment.
