Only have stayed and done diving on Dutch side. Staying in Orient Bay Area the closest dive op would probably be Octopus Diving located in Grand Case. From what I've seen they get pretty good reviews. The next closest dive ops would be in Phillipsburg around Great Bay. There are several good sites in this area. Great Bay really isn't a bad drive from where you are, ~ 20-25 minutes and just one main road as I recall. Octopus Diving has a shop there also. Octopus has a nice website showing info about all of the dive sites. I went with Scuba Fun 2 years ago and they were good - left my gear with them and scheduled some days on the fly as my back bothered me a bit. They were very accomodating. The only drawback with ops in this area, IMO, is they will get divers from the cruise ships, so you don't know what mix of divers you'll be with.
Ocean Explorers, in Simpson Bay, was a good op to dive with also, but it would be about a 45 minute drive from Orient Beach. Enjoyed the wrecks in this area, but liked the Great Bay Area for diving otherwise. Saw reef sharks on almost every dive.
Going back to St. Maarten in a month and haven't decided yet who I'll dive with. If anyone chimes in with good info about sites on the French side I may have to try that. I'm also thinking of going to Saba one day to dive.