I just finished my last contract on a ship (Musician) for 4 months of MX riviera where I learned to dive. We dove cabo about 4 2-tankers with Underwater Diversions. The DM's were great.
Visibility was about 35-ish feet. The water is cold if you are used to the tropics. for the 2-15-06 dive the coldest temp we had was 68F, warmest 74 degrees 10 days before. A full 6-7mm suit is nice, but we didn't use hoods and we were all pretty comfy.
You see a bunch of nice stuff. If you dive lands end theres a nice little channel by the rock where the sea lions hang out, a nice second dive at about 35-40 feet. The sea lions are used to divers and will come out and play. In there is a crevice with about 10 huge lobsters just hanging about. very good stuff.
I didn't get the chance to dive PV because of a passenger medevac out the prev night, but the shops in PV are adamant that they are "the best" on the pacific side. Let us know if you dive both cabo and PV which you like better
Zihuatenejo / Ixtapa is OK, but I didn't think it was nearly as good as Cabo. we did about 4 tanks on 2 different occasions and both times the vis for the first deep water dive was garbage. In Zihuatenejo there's a nice italian restaurant called Il Mare up the hill from Playa Ropa. Excellent food and good people. Best bet is to sit on the beach at playa ropa, drink margaritas and veg out.
Acapulco was where i did my cert, and there are a few nice places including an open wreck, but the pollution has taken its toll.
Hope that helps. What line are you on? you might be able to scare some of my friends who are still going to be on the ships
Happy Diving
Adam