Cat Ppalu, AquaCat and Blackbeards Sailboat Cruises are all run by the same company - all depart from the same marina in Nassau and all generally dive the same sites. Blackbeard's three sailboats are the least expensive, and the most "rustic" - if you are looking for lots of dives and the most bang-for-your-travel-buck, you might love it. The space is very tight and the accommodations are spartan. Some people don't like camping on a boat and desire more creature comforts. Cat Ppalu is generally chartered by groups only and has a bit more room - especially if you are going as a couple and want a bit more privacy than the sail boats offer. Also the sail boats can accommodate up to about 30 guests and they try hard to get as many of those slots filled as possible since the per-person cost is so low. Since the Cat Ppalu is chartered in its entirety for the week, the group who charters her has the option of selling off available slots - that why you occasionally see a single or double available, and that reduces the cost of chartering the whole boat, if you don't mind taking in a stray. The biggest, roomiest and most comfortable boat in the fleet is the Aqua Cat. They have en-suite bathrooms and individually controlled air conditioning, the boat has 3 levels and a big sundeck on top. It is the most expensive option.
But you will get in a lot of dives no matter which one you choose - with the possible exception of Cat Ppalu; IF you are unlucky and find the group who charters the boat decides they only want to dive once or twice a day and wants to do lots of shore excursions, fishing and kayaking - you might be at their mercy. Seems like most of the groups who charter the boat are dive shops, though, and after offering the trip to their own regulars, let the dive operator sell any unsold slots to solo divers or couples.
Diving in the Bahamas is pretty awesome. We went with them in March and had good vis and saw sharks (mostly reefies and a few nurse sharks) on almost every dive. Summer months are very hot, have very little wind (for sailing), and you have to keep an eye out for hurricanes. But I would go again. Trips with teens and single divers: definitely Blackbeard's. If I was going with a significant other (just the two of us): Aqua Cat. If I was going solo - or as a member of a small group (10-14 people): Cat Ppalu.
Hope this helps!
---------- Post added September 17th, 2013 at 02:24 PM ----------
OH - one more thing... you mentioned Nitrox. None on the Blackbeard's boats. I don't think they offer nitrox on the Cat Ppalu, either, but I think you can get nitrox on Aqua Cat for an upcharge. If that's high on your list of must-haves, it makes the decision easy.
