Cabo Pulmo is a a yearly or 2x year trip for me. Except for last year because of that little worldwide pandemic. I had to cancel my trip. I will be back in October of this year though.
Keep in mind that August and September is hurricane season and flooding DOES occur and the road to CP becomes impassable on the gulf side of Santa Cruz (a little town you will drive through with speed bumps that you will feel throughout your body if you hit them too fast!) If you make it past that one, you'll come across another section of road that also gets washed away in parts.
Definitely keep an eye on the weather.
If you do make it down there during that season, also keep in mind that it gets HOT. CP is an eco-village with a LOT of the community on solar power. If you end up staying at a place, A/C via a generator is available at some of them but they will charge you. And it's also something that they frown upon using a lot because you could knock out power for everyone at certain venues.
Diving in general MUST be done via local operations because their dive masters are specifically certified to take people into the marine park. (Local meaning CP and some operators out of SJD/CSL). This includes jumping into the ocean to go for a snorkel. There's a daily fee to use the park. That said, people still walk down the beach to the far end (north) to jump in and splash around but if you attempt it at the end closer to the dive shops, the boat captains will come to stop you and direct you out of the water (and radio it in to the tower).
I usually dive with Pilu (mentioned above). She is Cabo Pulmo Diving. Henri doesn't dive anymore but hangs out with their dogs. I usually visit or throw a dinner party when I'm in town so we have an excuse to socialize without being underwater!
I have also gone out with Cabo Pulmo Divers (the shop she worked for and still works out of). Their family is credited with being one of the "founders" of the place as far as eco-tourism, etc. But there are also family members that work at other places with names you can easily mix up with the others. (Cabo Pulmo Sport Center for one - Pilu uses their boats and Captain Luis is the bomb!)
I also have gone out with Manuela (Blue Passion Baja) who is super cool. Claudio, her partner is also a freediver and teaches courses for those interested.
There are other shops, Cabo Pulmo Watersports for example, that friends have used and have said great things about.
All of these shops are very close together and work from the same area of beach with one exception mentioned earlier:
Cabo Pulmo Beach Resort. They have their own separate section of beach where they launch from. My friend has rented bikes from there 2x (and got a flat 2x). I haven't used their actual dive services so can't comment on that. I tried to once but I was put off by the lack of help in trying to get it booked in the first place. (I was pretty much ignored while standing in the shop for about 10 minutes).
I don't have experience with La Paz so I'll stick to CP. Most all of the dives there are going to be around 55 feet. Maybe 60 or even 65. There's only one that goes down to about 80. If you leave the marine park and head south to Los Frailes there are a couple of dives there that are really nice and go past 100. Usually heading there means the weather conditions warrant a trip to that bay. Otherwise, lots of easy diving in CP. Immense amount of marine creatures. The increase in biomass over the years is astounding. If you like sharks, there are resident bulls and they're happy sharks and I've never NOT seen them each time I've gone.
Dive sites visits by boat/diver are limited each day/week. The first group to check in with the tower (with their DM) gets first dibs on the dive site. (El Vencedor with the sharks usually goes first). The start date of each week varies.
Two of my friends have taken their OW there. They loved it. (Though personally, I think they should have taken them in tropical Monterey, California!
and then do the easy fun dives in the warmer waters of Mexico).
Also to know: bring cash. The nearest ATM is an hour or so north. Lots of places prefer cash to credit cards (and you will save some money) (Peso or US$).
Hmm. Didn't realize I'd be posting a mini-novel!