Not exactly sure what you're looking for but here are some observations/suggestions.
First of all although Bonaire is great for corals/soft coral life, it's generally known as a coral/macro destination. There is the occasional shark spotting, recently a pod of dolphins in the channel between the islands, but about the only reliable "big stuff" is the tarpon feeding in the lights at Capt' Don's resort at night. Also to get to Bonaire from here, you're basically looking at an overnite in Houston (or now Newark) or a red-eye flight with a really long layover in San Juan. And avoid San Juan if at all possible, there's a lot of luggage theft there.
Cayman might be a better option, there's generally turtles on the North side, and a higher likelihood of seeing sharks feeding up the wall. And you'll always get mobbed by big Stingrays at Stingray City - in 15' of water so it's a long, easy dive also. And there's also tarpon there, usually you'll see Eagle Rays as well. And just millions of beautiful tropical fish and soft corals and huge sponges. And the water is so clear it's unbelievable, it makes Maui look average.
Downside to Cayman is that some of the really good dives start around 80-90' and drop down the wall. But there's also shallower dives and some of the operators only do them since they get a lot of cruise-ship divers there. So at your skill level, you'll still see some pretty amazing stuff. One of our best dives was Aquarium, laying on the bottom I was at 42' - watching little cleaner shrimp preen my cuticles. On AA, you can get there from here the same day although you leave pretty early in the morning and connect through Dallas and Miami.
If you want to see "big stuff" w/o spending the time to go to the South Pacific or Australia - in a weeks time, you'd burn up 3-4 days traveling each way, there's the Caribbean liveaboard option. We just returned from Cay Sal aboard the Nekton Pilot, I personally dove with as many as 16 sharks simultaneously one morning at a site called Big Hole. It wasn't the shark feeding - that was later in the week - but a dive site near there where they congregate. I have video of them where I'm as close as 2-3' away - check out my profile pic - On other dives on that trip, we dove with turtles(multiple times) got up close and personal with two large Stingrays, had two remoras basically try to molest us and saw tons of fish. And a couple days later we did the shark feed, not my kind of thing especially, but it was pretty exciting.
Downside of the trip is that some of the sites have lots of current, the vis isn't always stellar so good navigation skills are really important and you'd have to sit out a couple of the drift dives as they go from deep to deeper. Otoh, we also swam with a turtle and a ray at one site in 15' of water. And they also go to a site where the whole dive profile for the day is in 20-30' of water with a swimthrough that takes you into the center of a cay in about 6' of water. So you get a good range of different experiences. The typical diver on a Nekton boat is more experienced so they don't typically put a DM in the water with you, but they are available if you ask. Having said that, on our trip there was also a 12yr. old who certified on the boat. It's really a dive trip though, you can do 4-5 dives per day safely, but it's not really an "ultimate trip", the boat while roomy and comfortable is not exactly plush. The food is outstanding though, and the crew is very accommodating and friendly. It's something I'd recommend you do later when you have more experience and can enjoy it fully.
Another option might be the Virgin Islands, both U.S. and British. We spent a week on Virgin Gorda last April with a stopover in St. Thomas. The diving is good - not as good as Cayman - but pretty good, you'll see nurse sharks, turtles, lobster, barracuda and lots of fish in some areas. Also schools of bigger pelagics(tarpon etc.) if that's your thing. We did a couple of easy, shallow warmup dives on St. Thomas before going over to VG. We didn't see anything exceptional but the sealife covered the bottom. Good buoyancy skills were needed as in some areas there was nothing but coral cover.
The vis is kind of hit and miss there. One good dive is the Rhone, the BVI's signature wreck. The front is about 70' but the back - and to me more interesting half - is only in 45'. There's lots of soft corals and fans everywhere. It's done from either Tortola, Virgin Gorda or even St. Thomas as a day trip. The reason I'd suggest BVI is that in a week of diving, the Rhone was by far our deepest dive, most were in 50' or less including 4 or 5 good dives in 40' or less. I did one dive where I swam in thousands of baitfish in 20' of water while the big fish came in for lunch, it's was an experience like you see Blue Planet. So for someone of your skill level it might be a good alternative.
Downside is that you'll probably have to overnite both ways in St. Thomas and take a ferry over to the BVI's. The upside of that though is that you have no no-fly restrictions when going between the islands. We dove until Friday afternoon and then ferried over to St. Thomas on Saturday for flights home Sun. morning.
I've also heard the best diving in the USVI's is on St. Croix, but I've not been there. There is a direct flight from here that gets you there around 9PM after flying all day.
hth, join us at one of our AZScuba meetings as some of the regulars went to the BVI's and we've done a lot of diving elsewhere. Also we maintain our group forum here:
http://www.scubaboard.com/forumdisplay.php?f=458
P.S. Just saw your post, a group of us are planning to go to San Carlos from here to see the Hammerhead migration in Oct. There's thousands of them. You're welcome to join us, it's a long weekend trip. But know that you have to get deep under them and they're sometimes aggressive. Personally not the type of shark I get too close to.
!)
