Asked and answered more times than "What is better, PADI or _____"
Look at the botttom of this thread for a list of automatically generated similar threads. Go over to the "cruise ship" forum and

there with the word
Roatan.
There are all sorts of ways to see a small glimpse of Roatan. Many will go to AKR and do the Dolphin Dealie. More than a few will select from one of the many West End
day dive operations that line that zone. (Bananarama, CoCoNut Tree, and others). A few will find Subway Watersports. There are some others that are on the list, too~ some even go through all the gyrations to dive the shallow Prince Albert Wreck.
Which one is right for you? Do some reading.
What are the "must do" dive sites? Again, a question quite well answered, but the actual bottom line is this... Any dive op will treat you as if you are there for your first day of diving. Most such cruise ship divers, and unfortunately you'll be painted with the same broad brush- most of them need some serious watching and weight adjustment. Most would surely improve as the week goes on, but they'll be in Belize by tomorrow, and likely asking the same questions.
The choice of dive sites are a function of the above distasteful paragraph. They will take you where they will take you. A legal operation simply cannot take you to highly vaunted Mary's Place because you will not have had the time to go through the training process all dive ops have ascribed to in order to preserve the site.
Otherwise? they'll take you out for a nice little glimpse of what Roatan has to offer a diver who sticks around for a week. It's just not a place you can understand or see in two dives.
Do a little research here, go and have fun.