Hi there,
We were out there about 2 months ago for a couple of weeks.
We dived with both Dive India (Island Vinnie's) and Barefoot Scuba. As the guy says above the dive shops are in fact about 100m from each other. Prices are nearly the same.
Personally I preferred Barefoot, mainly because they were a little less busy than Dive India so I could get on the dives I wanted to. And because the boats weren't so crowded. But either way they take you to the same sites and are all good guys.
Island Vinnie's does good dive packages if you want to role up your accomodation, food and dives altogether.
But, the food isn't as good (not that it's bad, but there are a couple of great places to eat: Wild Orchid and Emerald Gecko) as some of the other places on the beach. In my opinion you'd be better to go and stay at one of the beach "resorts" nearby and wonder down to the dive operators. We stayed at Emerald Gecko and then cycled down to the dive operators in the morning.
As to the dive sites, I actually thought most were fantastic. Not sure what the silt comment was about, maybe we were really lucky. But when we were there visibilty was 30m plus, and there was fish teaming in Button Island, Minerva, Dixons and Johnny's.
The diving isn't all that challenging, but if you want to gaze at a myriad of colourful fish and startling colourful coral then you won't go wrong!