The beach is average. It's not a beach like say east-cost Florida. Beach is not wide/deep like that. It's attractive, palm trees and the like, and the facilities are pretty good. We were not disappointed.
FOrget the ships excursions!!! Save yourself more than 1/2 that cost (and see more of the island too) by simply getting off the boat and hiring one of the waiting locals for the day. On your way back have him take you around the island, On the back side is a small village with cheap shopping.
I was trying to decide between those two beach trips in Roatan as well when I read somewhere that there were sand fleas at Fantasy Island and that at Tabyana they treat the sand so we picked that one. We had a great day there and I would go back again.
We did not do the beach timng in Roatan...we hireda cabbie and cruised and explored the island. However, we say alot of our fellow cruisers that had bites all over their back. I would follow above advise. Does it help if you lay in a chair and not on the sand?