I love diving both Cabo and PV. I was there most recently last September (and will be in Cabo at the end of August). The water was in the mid-80s. I like Underwater Diversions in Cabo. However, most ops there are pretty good. It is a quick ride to the dive sites. PV is also good diving. Even though its a cattle boat, I like Villarta Adventures. I've been with them on about 6 trips to PV. Even though the boat includes swimmers, snorklers, etc. I find its a good dive, especially given that its a vacation dive. The DMs have all been outstanding. The boat is big and comfortable, which is nice for the long ride to the dive site. You'll have a good time with them.
There is no diving in Mazatlan. I've been there on a bunch of cruises and have never found either diving or a viable place to dive.
If you've never been on a cruise, there is lots of good info on SB relative to diving while cruising and cruising in general. If you need some tips, PM me.