The NCL one is complete shit -- at least the one I visited in 2017. I have not been to the Princess or Royal ones, but others criticized them, so I am surprised to see that you are positive on them. Is there really room for everyone on the Princess island? The NCL one was wall to wall people.
The only cool thing about the NCL island was that they placed large items at the bottom of the sea in the very deep areas, so reefs would form around them, and it attracted a lot of fish. So the snorkeling wasn't bad. However, you had to swim a good way out to get there, and had something happened to me, nobody would've seen it and I would have croaked. There was also a strong current attempting to drag me out to open ocean. The only reason I felt mostly comfortable was because I had fins on, plus a yellow snorkeling belt (looks dorky but is VERY useful for snorkeling, and is used in place of a life vest). So with that stuff on, it was hard to either drown or be unable to swim to shore. Once I got away from all the people and out into the deep area, it was a decent solo snorkeling excursion. But the beach... a crowded mess.