Yes Don, there are now two operators providing nitrox, and only one offering anything other than 32% (ourselves). In any case, unless you're really trying to optimise your nitrogen uptake you'll use 32% or 36% for all local dives. Assuming you're an average recreational diver, you can use 36% for almost all your dives as it's usable down to about 95' on a ppO2 of 1.4. In reality, 32% is fine to reduce your nitrogen uptake enough to give you pretty extended no-deco bottom times. We produce 28%, 32% and 36% by continuous blending and have them available all the time; other blends can be produced to special order but unless you're into technical diving you won't regard them as economic. If you're not a strictly recreational diver then I assume you'll be coming to us anyway.
If you want to dive the Blue Hole you can use 28%, although one of the main boat operators going there doesn't allow any nitrox on that dive. Again, in reality air is fine for this dive if you use nitrox for the two following dives. If you use air for all three you can run into bottom time limitations.
So don't trouble yourself too much about nitrox mixes. As to dive sites, they're all similar in that they're all on the same barrier reef, but they vary considerably in detail. One of those details is what interest there is at different depths, another is how water clarity and surge vary across sites. Only a good local divemaster will be able to say which of several sites will be best to dive on any particular day. In any case, unless you have your own chartered boat and private DM (possible, and some people do it, but expensive) you'll have to defer to the majority view when it comes to deciding which dive site a particular dive will be at. If several people have already dived what may be the best site for that day and don't want to go again, you won't go there.
Operators do differ in how they schedule dives. Some plan the dives up front and tell you where you'll be going, others do it by a democratic process on the boat just before departure. Some divers prefer the prescriptive approach, others prefer to have input to the process. Choose your operator accordingly.
Last thoughts. You can buy nitrox from other operators who buy it from one of the two producers. If you use one of those operators, make sure they have an analyser you can use (unless you have your own). I can tell you that having had two analysers destroyed in as many months by people getting them wet (in one case, actually dropping it in the sea), we NO LONGER lend analysers to other operators. Use our analyser at our premises or not at all.
The other thing is - where are you staying, and do you have a dive operator already arranged? That will largely determine the range of sites you're likely to dive. Fuel here is so expensive the boat won't repeatedly go to distant sites unless occupancy makes it economic. Translated, that means that if you like small groups you won't be doing many distant dives unless you're prepared to pay for them.
