If you're going that far out, I'd recommend Amigos Del Mar, http://www.amigosdive.com.
In fact, I'd recommend them for any dives you do. Good people, lots of local experience and they've got the best dive boat on the island for long trips, IMO--a Pro 48. Good staff as well and a bunch of smaller boats for close-in reef diving. I'd also recommend them for a trip out to Turneffe. The Elbow and The Aquarium are really memorable dives for me. It's a long way out to the Blue Hole and Turneffe. If there are any seas at all, you'll be glad you're in a big, comfortable boat. For what it's worth, and this is my personal opinion, the Blue Hole's not that big a deal. There are a lot of other much more beautiful and interesting dives to make from AC.