Parrothead: If you are looking for LOTS of activities, I would think Paradise Beach or San Francisco Beach would be the choice. As LHP has mentioned they have such things as the banana boats, some iceberg-looking floating thingie that kids can climb on, kayaks, parasailing, etc.
I have never seen anything (like that) going on but snorkeling and diving at Chankanaab, aside from the Dolphin Encounter. But it IS great for that, if that is the activity you want. And the food is pretty good. I can't vouch for the drinks, because I usually stick to Diet Coke or beer.
Cozumel is one of our favorite places....I don't think you can really go wrong, no matter which you choose!!