Per the excursions we've been on,
dcl sanctioned excursions will always ask you to wear the snorkeling vests - helps them see you as we'll. I don't put any air in mine. We went on the double doubloon pirate ship one and it was excellent. Alot of the snorkeling areas are shared among excursions. We had no rough water and no sea sickness, can't imagine how switching excursions could have too great of an impact in that!

also, all the areas we went to off a boat are going to be deep? That's kind of the point. I could go down to nearly the bottom with fins, but I'm not super coordinated with the snorkel so I just dove in here and there. We saw turtles, rays, all kinds of fish. I'm sure you will have a great time no matter what you choose!!