Two things to be understood. Reviews in places such as here or TripAdvisor tend to be more numerous for the busier operators. Look for quality, not quantity, unless you like being with a large crowd. And secondly, many/most operators work with local hotels on a commission basis, and there are several exclusivity arrangements that you won't be told about even if you ask. Take any recommendation by an hotel or anyone who could stand to gain with a large pinch of salt.
Two further points on commissions. The generally prevailing rate is 20% of the gross rack price, or sometimes the actual price charged if a significant discount has been given. But there is a tendency to offer more than this 20%, sometimes markedly more, to "steal" business from other operators. Remember that you, the customer, generally know nothing of this. Clearly if you go directly to the dive operator and don't involve the hotel in any way, there'll be no commission payable and the operator will be better placed to offer you a discount.
The final point is that not all dive operators do business on this basis. At least one highly regarded one pays no commission, so is never mentioned by hotels expecting it. And a few hotels don't demand commission, so their recommendations may be more objective.
My list, going north from VH:-
- Belize Diving Adventures (Everette and Enes, Belizean husband and wife team, highly experienced)
- Ramon's Village (a little pricier than some, and possibly the better for it)
- AquaDives (now the largest operator, some excellent divemasters, very good boats including the largest on the island for atoll trips, used to have a poor reputation that's no longer merited, the only operator in the whole of Belize capable of supporting serious technical divers)
- Bottom Time (long established and well regarded but with a very low profile)
- Ambergris Divers (well established, nice boats, some good staff)
- Island Divers (new boy on the block, operating out of Protech's previous premises, Rudi is a new instructor but a well established and popular divemaster)
- Amigos del Mar (traditionally the "gold plated" operator here, flagged a bit after their big boat spectacularly blew up and sank last year, but they've just replaced it with a very smart brand new big boat that's around the same size as AquaDives', on the way back up)
- Ecologic (been around for two or three years, some good staff)
- Chuck & Robbie (two person operation that's acquired a very high reputation, don't pay commission), and lastly
- Patojo's (only service their own hotel guests and people who go to the trouble of going to them, but very highly regarded by people who take that trouble).
I know I've missed one or two minor players, mainly because I can't remember their names and know very little about them. But as I said above, I'd willingly dive with any of these operators (if they gave me the dive free!).
