I've done some snorkelling from Catcha and from Xtabi. Is it world class ...... no. But I love to snorkel so it's all good and there is always something to see. I bring my own gear, I like to know it fits properly.
If you want some FANTASTIC snorkelling, I would give Famous Vincent a call, he will take you out to the reef and guide you through. It's about an hour long and we have seen some pretty great stuff out there. Turtles, rays, eels, octopus, lobster, etc. Vincent seems to know where everything is down there.
If you want to do something SUPERFANTASTIC, take the intro Scuba class with Ken and Sabine at Dream Team Divers and go for a dive!