I think your best bet is to do the it through the cruise line.They did use Sand Dollar in cozumel.I heard mix reveiws about them but I had a great time with them.Plus they supply transportation.In Grand Cayman they used Don Fosters.They were good.Had 2 good dives.Remember if you book through the ship you will be back in time or they will get you to the next port.They also provide transportation so you dont have to worry about getting taxis.Alot of dive shops will not cater to the cruise ship diver.The prices are about the same once you add in transportation.I think you will have a good time no matter what shop you use.The rental stuff is hit or miss.I bring my own.The wetsuits were alittle beat up.If you have any other questions just send me a message