I'm sorry for you that Manzanillo isn't on your port list, it is the best of the bunch, I speak with cruisers regularly and their reports are that;
Acapulco, turists are restricted on where they can go due to crime, wasnt a fun stop.
Zihuatanejo , nice but I have never heard that there are any scuba shops there, snorkling ok but better in Manzanillo
Puerto Vallarta, corrupt, overpriced and too touristy, I dove there & not impressed
Cabo San Lucas, I dove there and it's over rated too , sand falls is just a little bit of sand falling out of a rock no more exciting than a spilled salt shaker, the seals are fun if you've never dove with them before, if you go out on a panga be sure they have a ladder to re enter the boad after the dive, mine didn't
Manzanillo;, ship wreck in 26 ft of water, 10,000 yr old coral reef , beach dive last week 76 deg water & found a sea horse, turtles seen often, whales have been spotted for the past month