Grumpy and Happy purposely have the "best ladder in Belize.". They do custom trips and supervise well.
Olivier is also great, and I love Genie at Coral Divers.
I have not done Blue Hole at all, but understand that snorkeling there isn't that interesting ..... However and further told that there are a couple of other excellent snorkel spots included in the Blue Hole trip so perhaps it would be worth it to go!