For a recent reviews of Punta Sur park see 'The Original South Park' story on this Cozumel vacation
They also have a review of Chankanaab
The island looks a million times better than in January - we've had a lot of rain since then and it is green again - yes, you will see some dead trees and some of the piers ar still being rebuilt, but otherwise you'd probably never guess a hurricane was here less than a year ago.
The beaches are in excellent shape now - Paradise Beach is a good option.
Those that are serious about snorkeling will find boat tours are much better than shore snorkeling as the reef near to the beaches is still recovering - not just in Chankanaab but pretty much everywhere.
Two I can recommend are the catamaran tour from Paradise Beach
or the Fury Catamaran tour
Hope that helps!