I have used Horizon Divers (24 dives) and Ocean Divers (22 dives) several times. They both operate the same. On the reef they tie to the ball, say pools open, and be back in an hour. OD has big boats but will go out as long as they have 2 divers. I have done several dives with them in the 2-6 diver range.
HD has a big cat and a smaller boat. I think they need 4 to go. They start slightly later. My experience has been that with HD you can make requests which they will try to honor. For example they took me to City of Washington wreck. With OD it is more of a preset schedule. However, we had two on OD once, both were fairly experienced at the time (DM candidates) and they asked what we wanted to do. Went to the outer edge of the reef and did a couple drift dives.
If you wan to go to Spiegel/Duane/Bit than with HD you can rent a DM if you want. Assume same for OD not sure. I often travel solo and I did not want to instabuddy on the duane with HD for the first time. So rented a private guide. Great dive on the Duane.
I usually stay at the holiday inn at the Marina or the other hotel. Easy walk to either boat. Have also dove with Bluewater and Sea Dwellers. Did not like the Sea Dwellers boat as well. Did 4 dives with Bluewater (2 on speigel and then two deep drift dives without returning to shore). Nice folks but I found that a bit agressive and I spent the last drift dive way up the water column nursing my NDL.
I like to drive from the airport at Miami and park my car and then not turn the key until I get home. Both HD and OD have their shops and boats at the Marina. They also go out twice a day. Doing 4 dives a day is practical if you want. Both allow you to store some gear if you want.
In Largo my experience has usually been not to be blown out but it has happened. If you are hungry to get wet you can go play in Jules. Not a beautiful coral reef but more interesting that a quarry or freshwater lake. You will see some critters (lobsters, etc) and some types of tropicals.
Finally both the HD and OD have wide boats. They have rarely been completely full. Usually half or even less. But I have never felt crowded on them. And in the water I just choose a vector different from a class if there is one.
