If you're looking for bigger sea life, I would agree with the comments above that Belize on a liveaboard will give you more opportunity - on my trip there we saw reef and nurse sharks, a pod of dolphins, tarpon, big grouper, turtles, etc. The East end of Grand Cayman will give you more of the option to see reef sharks and the bigger grouper/snapper, as well. Bonaire seems to have more medium sized fish, with the tarpon at different sites and some big grouper/snapper on the Hilma Hooker wreck site being exceptions it seems - if you want bigger there, I would suggest checking into the options to dive the East Side - you will want a guide since it is windward and not the easy shore diving found on the west side.