I have dove with Horizon, Ocean Divers and Rainbow. I had significant problems with Rainbow when they had the operation in Islamorada. We went out on a six pack boat from the Chesapeke resort. Both of the tanks they provided had less than 2000psi, one was 1435psi according to my log book. They have a DM in the water at all times, and I asked if he would trade one of my tanks for one of his as I assumed his consumption was lower than mine. He refused saying he needed the extra air in case of emergancy. There was a cute girl from new your and a guy that came with her as a "friend" the young dive master was too busy flirting with her to care about my lack of air supply (it was shallow reefs, but it did shorten my dive). I hit the water first and waited like 5 mins for everone else to hop in, once they were down, we started off, the younf DM finned me in the face and I lost my mask. I found it after a short search, but they left me behind. We were shallow so I finished my shortened dive. I obviously came up before everyone else. The DM and the Captain were uninterested in my shortened tanks or the fact that I was forced in to a solo dive. On the second dive, I just quitly prepared my gear, when the pool was open I hoped in and dove solo again as I felt that I had no buddy and If I needed assistance, the DM would probably not notice.
I own a business, and I know it is possible to have a single bad experience. I was planning on going out again, but when I asked the Captain where we might go, he said "you will know when you get the dive briefing". I did not dive with them that afternoon, next morining I drove to Largo and dove with Horizon.
I dive with Horizon and Ocean divers. Horrizon usually leaves at 9 am so if I am leaving that day, I usually dive ocean divers as they leave an hour earlier and get back sooner. Both oporators are top notch. This past weekend, I took the Speigel Grove Research course through Horrizon, but Saturday morning our intructor from Horrizon, my buddy and I rode with Ocean Divers to the grove. There were not enogh divers for Horrizon to go out, so the worked cooperatively. The ocean diver crew and horrizon diver instructor were obviously very friendly and I have a lot of respect when businesses in compettion can work together like that. Both Horrizon and Ocean Divers are fantastic. What I have done in the past is dive ocean divers in the AM, and Horrizon in the PM, because of the different start times, you have a little more time between dives to catch a bite to eat and relax.
I am sure there are other great oporators in the keys, I do not think they would survive long in such a competitive environment (Rainbow's Islamorada location is now closed), but you can not go wrong with Horizon or Ocean. One more thing, if the seas are rough, the Ocean Divers boat is a little drier, but the Checca View from Horrizon has Capri Sun to drink between dives.
