This is a super old thread, but maybe you didn't get to go yet because of the pandemic?
For snorkeling, I like Cozumel. Most airlines fly to Cancun and you can then take a cab and ferry to the island. The only problem is that Cozumel doesn't have a Hilton chain hotel as far as I can tell (I wish it did since we're Hilton Diamond status.) There is a really nice Westin there, though, and prices are very, very reasonable right now. It works out to be cheaper than all inclusive unless you drink like a fish, and even then it might be cheaper. The hotel provides snorkel gear for free and you can snorkel right off the shore and see plenty of fish, especially if you go under the pier over to where the breakfast restaurant overlooks. There is also great snorkeling at the Columbia reef and other locations such as the shallower clear waters such as Xel-Ha (basically pronounced Soul Ha) if you want to book a private boat tour, which is again very reasonable right now, go out with Cuchi on Mystic Snorkel.
Good luck in your adventures!