We just got back from San Pedro. We went with Amigo Del Mar on their Blue Hole trip with 16 divers and 6 snorkelers. One of us dove and one snorkeled. They have a nice boat, comfortable and it has a head (bonus!). The blue hole itself is a great snorkel, worth the trip by itself. However the second stop at Half Moon Caye was next to useless--4-5 foot visibility.
We were told that that this is normal for that area. The caye itself is cool--frigate birds and boobies everywhere.
The third snorkel stop they dumped us off in 50 feet of water and told us to swim to the reef 150 yards away in a moderate fast current. By the time we got to a snorkel viewable depth (yeah with good vis you can see through 50 feet of water but what is the point?) we were about 1/4 mile away from the boat and still drifting away (the boat was moored). Still, we saw some good stuff. Also the boat came to get us so we didn't have to swim against that current. However they never told us they were going to do this which caused some concern in our group as we realized the speed of the current.

The divers reported all 3 dives to be good to great. They saw tons of sharks in the Blue Hole and at Halfmoon caye they saw spotted eagle rays and swam thru some tunnels.

Overall, great for the divers, but just an ok experience for the snorkelers.

Also, one of the other snorkel/diving couples told us they had gone on an Hol Chan/ Shark Ray trip where one had dived Hol Chan and the other snorkeled (both snorkeled Shark Ray). They had booked the trip thru Blue Hole Dive Center but it was on a private dive masters boat. The diver had a great time- because Hol Chan was full of people that day they went outside the reef and dived in 60 feet of water rather than the 30 of Hol Chan itself. However, that left the snorkelers with no boat access--they had a great snorkel (Hol Chan is very nice) but were left to sit in the water while they waited for the boat to come back for them. It took so long that the snorkel guide climbed up on another companies boat to get warm and the rest of the snorkelers soon followed. Sounded like they would have had a better time had they been able to get back into the boat in a timely manner.

Have a great trip!