Hey Rescue Diver 68,
I've had routinely good experiences with Ocean Divers. Turns out I have dived with them every December since 2004, 5 years. They offer 4 dives per day (weekends and weekdays) in addition to night dives Wed and Sat. I usually fly down on Friday, drive to Key Largo, and then do 11 or 13 dives through Monday morning or afternoon. This allows me to get in 4 wreck dives in addition to the reef and night dives.
They are very reliable and have never cancelled one of my dives due to conditions but occasionally have had to change sites. Their large Newtons are quite stable, even under adverse conditions. There is protected space for even the worst circumstances. They guarantee they will go out with a minimum of 2 divers. I have gone out to the Duane on Sunday afternoon on at least 3 occasions with only one other diver, that's service. The maximum capacity of the boats is somewhere in the low 20's, that does not seem crowded. In December, the number of divers is more usually 8-10, luxurious space.
Personally, I cannot see diving with 30 something divers off the Horizon dive barge. I've seen it many times, particularly in the more seasonable months, and it is not a pretty picture.
Ocean Divers reliably supplies Nitrox 32 at only a $6 upgrade over air, very handy for the dives on the Spiegel and the Duane. They offer a multidive card that I always take advantage of that lowers the daily cost of diving. Their website is very useful and I would encourage you to peruse it
DIVE KEY LARGO WITH OCEAN DIVERS - SCUBA diving, snorkeling, PADI diver training, IDC & CDC - Instructor & Career Development Center
The most startling fact of diving in December is the water temperature. Most years, the water temp has been 75-76 degrees. In 2008, the water temp was 73-75 degrees. I was very happy with my 5 mm full suit and hood. This paid particular dividends on the afternoon and night dives.
Best of luck to you on your trip to Key Largo.
Good diving, Craig