Howdy!
Well that depends on how much time you have and what the rotation schedule is when you get there.
For example, I landed Nov 19 (monday). I did not get to dive at the wreck site until the 24th (Saturday).
The main site that everyone wants to go to is the wreck: El Vencedor. The bull sharks often hang out there and that's where numerous fish and moray eels (green and jeweled) hang out. On the last visit I saw 3 guitar fish has we descended as well as at least 10 sharks in my field of vision. Earlier this year there were some slugs too: a couple of yellow tylodina on top of one of the wreck parts.
It's one site you will probably want/need to dive.
After that, the other major sites are El Bajo and Los Morros and Esperanza - really nice reefs and rocks with a lot of life to be found both small and large. El Cantil can be nice too. A couple of these sites are divided into north and south.
Towards the south of Cabo Pulmo, there's the sea lion colony which is nice if you're into seeing those guys. Casitas which has some swim throughs, and La Islote which can be really pretty. Often there are creatures hiding in the rocks or there might be a nice sized group of jacks nearby.
There's one site called Mario's Reef or Le Cien (i think that's the name). It's a deeper dive and somewhat barren at times but this is also a location where the bulls sometimes hang out. Each time I've been I've seen at least a couple.
On this last trip while sheltering from the wind after diving La Islote, we were at a site called Pedregal. It's not one of the popular ones. I dove it for the first time this year and loved it. Lots of large boulders with crabs skittering between the cracks. Some fish but plenty of coral with more small crabs and even a few frog fish hiding inside. When moving deeper and up to the boat there were some larger rays (diamond I think) as well.
You're supposed to be allowed one "pretty sister" a day and then you have to "suffer" with another site. The first 4 above are going to be the popular ones. But all of them have a good side too!
There's also an option to go dive outside of the park at Los Frailes. There are some spots similar to the reefs in the park and once in a while a nice shoal of fish will be present. One site here has a deep trench you can dive that goes beyond 100 ft. Not much to see down there without a light and nothing I ever saw in that area was something I couldn't see at a shallower depth.
It seems many operators will dive 2 tanks per day. However if you want more, then just ask. For example Pilu (Cabo Pulmo Diving) only does 2 herself, but she will contract out another DM when I want do to more in a single day (and I do like the other DMs so I'm not bothered by this).
I'm currently trying to upload my photos from this visit but if you'd like to see them:
kumi's moblog
(in reverse order)
Hope that helps!