My family and I are planning a trip for late December and are looking to do quite a bit of scuba diving. Mexico appeals to us because it is easy to get to, but we have been to Cozumel several times and are looking for an alternative. The diving there was great, but we would like to go elsewhere, and are hoping to find great diving elsewhere in Mexico. Any ideas or suggestions are welcome!!
Here are some generalizations based on my personal experiences.
Puerto Vallarta - cold water, not terribly known for great diving. You'll have to really work at it and wring the place out to make the diving worth while
Cabo - same as above (now get to the sea of cortez side and things are different, but its not easy access and accomodations are sparse)
Cancun - some pretty okay diving, but if you're going to cancun, unfortunatly you're in cancun. You make the call if cancun is okay or not for you to hang out in.
Isla Mujeres - same diving as cancun, infact the better dive sites are when you leave the isla area and dive the cancun sites. Great small island, unique experience, not great dive ops serving the place though
Playa, Akumal, Talum - decent diving, each area has a little bit different things to do and see
Cozumel - quality of diving beats all of the above, just plain consistently above average diving no matter what you do, some of the best dive ops you'll run into are based in Cozumel. Few places seem to have so many dive masters with over 10,000 dives then Cozumel.
My 2 cents
Keep in mind all the above are generalizations, time and circumstance can turn any mediocre dive into a great one. All it takes is a manta or whale shark to show up when not expected and you're on the dive of your life!