I have photographed bulls in the Bahamas with JASA on Wetpixel trips, both at Walkers Cay and Jim's site "Edge of the map" - as well as seeing them at other sites, when they have turned up. I have only been to Walker's the once (March 2006) and while there were several very big bulls there and we got nice shots, people commented that it wasn't the dive it was when the island was open. Another 4 years on, there could be even less.
End Of The Map has lots of bulls, particularly at the right time of year (I forget exactly when). But the bulls there are smaller and sleeker than the massive ones at Walkers. The setting is probably prettier, with better viz that Walkers. Although Jim generally doesn't go to that site specifically for the bulls.
Fiji seems to be the most reliable.
Alex