The major draw for divers at Isla San Pedro Nolasco off San Carlos tends to be opportunities to dive with sea lions in water with frequently decent visibility. It often is a remarkable experience. I never tire of photographing sea lions when diving the island on days when members of the colony are in engagement mode. In terms of species diversity, many local dive sites produce better than the island. I've got one particular favorite, but can't seem to get either of the dive ops I use to drop me there.
Diving in the immediate vicinity of Puerto Penasco (Rocky Point) is usually focused on Isla San Jorge (Bird Island). The big attraction is again, sea lions. I suspect the island has more sea lions per square foot than most places on earth and the pinnipeds tend to enjoy interaction with divers. The major drawback to diving with sea lions there is visibility. Daily tidal flows are extreme in the area. The tidal flows tend to stir things up and generate lots of current.
There is a livaboard dive boat operation in Puerto Penasco. I've never had the pleasure of spending a week on board the boat, but I've several friends who've had good experiences with the op. They've done trip down to the Midriff Islands in the Sea of Cortez.
Puerto Lobos is probably a lot like what it was like diving in the 'old days' in Mexico. It's basically a fishing village that's seen some 'limited' real estate development since the village got electricity. Diving is all local and Lobos has not seen large amounts of diving activity. At an hour and a half south of Puerto Penasco, it's still far enough north to see as significant tidal flows, but has fewer visibility issues than Penasco. As a rule, species diversity increases if one begins on the north end of the Sea of Cortez and moves south. I've been impressed with how much different the Puerto Penasco and Puerto Lobos marine ecosystems are. Drift diving there is a hoot! There's lots of stuff to see.
If you're interested in seeing what's in the waters off the coast of Sonora, there are lots of photos on my website:
www.cortezbluephotography.com
-AZTinman