I cannot recommend Went End Divers enough. They picked us up from the cruise ship in a van, took us on 2 great dives, and brought us back. Between the dives, we got to walk down the cute little West End street and have some great mexican food from a little stand. Depending on your ship schedule, you may be able to get a 3rd dive in. One guy that was diving with us from a different ship stayed for the 3rd dive.
We also dove on that cruise itinerary in Cozumel and Belize. All in all, like the best dive cruise itinerary that we could afford, both in terms of time (7 days) and money ($649 for a balcony room.)