I mostly echo what Tim says. I will say that the Brac does have some great dives. The wall on the Brac does start at 60 where on LC it starts at 20. I have been fortunate to see some peligics every time I've been to the Brac. I've always seen eagle rays, always seen sharks, (not just nurse) black tips, bull, lemon, and hammerhead. I've seen Manta and dolphins. On Provo you will most likely see these things with more regularity like on nearly every dive compared to dive trip. When diving the Brac we always seem to get to LC for a number of dives as well. LC has the most stuff in MHO
other than the peligics, more colorful sponge and more species, more little things like the Flamingo tongues, lobster and shrimp species. No doubt about it T & C has more bigger value, when last there we saw the largest stingrays I've seen off West Caicos.
I also think that the viz is a bit better in the Caymans. Viz in Coz can be mind boggling, but I've seen the viz at LC reach over 200ft, you just have to hit the right weather.
I do believe that Caicos Adventures should be your choice if you go to Provo, you'll not be sorry to have chosen them for diving. Fifi knows the area, and will take you to some great dives
Dive Safe,
Caymaniac.