I will be going to Roatan, Costa Maya and Belize for the first time in January. I will be on NCL gem. I am looking forward to it.
If you want to go on NCL, I recommend the new Norwegian Epic. I think it will be a very fun ship.
Also - you don't say how old you are, or why you want to go to Roatan. More details in what you are interested in will help us help you a lot.
In fact, many ports in the Caribbean offer similar things, so Roatan may not be a necessary decider, which would open up different ships.