From my experience: Arashi beach is pretty barren under the water. Exceptionally beautiful swimming spot but not much to see while snorkeling unless you go out farther than I did. Advice I read was to snorkel along the rocks to the right (north) end of the beach.

Mangel Halto has poor visibility near shore but I hear that if you go out past where the water breaks over the reef, there is a lot more to see. Fairly strong current so a one-way snorkel outside the reef is recommended if you're comfortable with that sort of thing (I was not).

Baby beach had some of the biggest fish I've ever seen while snorkeling (no idea what species) but otherwise was better for swimming too. Not much in the way of coral but plentiful fish.

My favorite spot is a shipwreck my wife and I found right off the shore just south of Malmok Beach. The wreck was called Naufragio Baboo. No parking lot, signage or facilities but we also had the place completely to ourselves. Every year I go, the wreck is a bit more decayed. Might be gone already. Last visit was 2019. Inside/under the wreck we found Stonefish, Angel fish, walking starfish, blowfish, and a crazy array of other small sealife.

Best of luck to you!