TC diving out of Provo is actually quite good as they normally go to West Caicos and even French Cay if conditions permit - but boat rides are long so you blow most of the day even on a 2 tank. Lots of good restaurants in Prvo too!T&C diving out of Provo just meh. Topside pretty basic. Cayman Brac Beach Resort is very well run, great boat diving. Same folks run similar op on Little. Both are all inclusive, great diving. On GC we like Sunset House. GC strengths are variety of topside activities and great shore dives to complement boat diving.
Grand Cayman has more options for diving including great shore diving - plus boat rides are short so you can still have a good part of the day for non-diving activities. Lots of restaurants, shopping, great beaches and good snorkeling spots for non divers.
I was just in Brac last November and the diving was decent, but not spectacular - typical Caribbean. I wouldn't say it was better than Grand Cayman (especially GC East End) - in fact, several southern Brac sites had pretty badly bleached brain corals. Perhaps I was jaded as I had just come back from Rangiroa/French Polynesia which makes most of the Caribbean pale in comparison in terms of bio-diversity and health of corals.