Where are you staying? Recommendations for the East End will be different than the suggestions for someone staying in the Several Mile Beach/West Bay area.
There are a many really good dive ops on Grand Cayman and everyone has their favorites, the competition is too heavy for a mediocre operation to last long in that environment. Even the larger ops like Red Sail make sure that they have large roomy boats so as to avoid cattle boats. I have heard that Red Sail has been offering a free sunset cruise if you are diving with them - don't know that for sure - but it might be worth looking into because it sounds nice!
A few places have house reefs and they will give you unlimited shore diving (weather permitting) while you are boat diving with them if that is of interest - these examples include Sunset House (Sunset Divers), Cobalt Coast (Reef Divers), and Lighthouse Point (DiveTech).
If you have a dive buddy and just want to do some inexpensive shore diving, check out the dive ops at Macabuca (Sundivers) and Coconut Bay Condos (Stingray Watersports).
If you want to do 4 good boat dives in one day (or just a 2-tank boat dive in the afternoon) then Ocean Frontiers at Compass Point on the East End is the best option - but that is a rather long drive if you are staying in the 7MB area.
One thing we try to avoid is getting put on a boat that is primarily serving the cruise ship passengers, but the cruise ships are on a different schedule so that doesn't usually happen. I have never dived with Don Fosters, so I have no personal knowledge, but I have heard that they do a lot of cruise ship business. I know that Red Sail works with one or two cruise ships, but I have been told that they use separate boats for the cruise ship crowd.
If you are in the 7MB area, most dive ops will pick you up in a van or on the beach in a boat; ask your concierge or rental unit manager if they have a relationship with any dive ops. If you are staying in a more "out of the way" location then you may need to drive to the dive shop or the marina to meet them.
We have had very good experiences with Cayman University Divers, they have a beautiful, small boat and offer personalized, professional service, but as I said, there are many good dive ops available. Have fun!