Alucard I would always suggest people give SXM a dive or two if they be there... definitely not THE best, but also not BAD either. I quite enjoyed some of the sites there. When I was living on the island a couple years ago, there was very healthy reef, even if somewhat short of large fish.
While Saba next door is on a different scale and IS a destination dive location, the diving on St Maarten is not worth missing. IN MY HUMBLE OPINION: If you are there, you are crazy to not make an effort to check it out. That being said, there probably are many better diving locations available if you are looking to travel specifically for the diving...
Despite never having worked for them, I do have respect for Ocean Explorers (who Frostfire went out with originally) and would count them as 1 of only 3 operators on that island I personally KNOW and respect enough to go on charter with. Also... If I had to choose a Caribbean operator for teaching family, I would trust them teach my family members to dive based on my personal experience with them at that time. I never did get over to the French side for diving, so MY experience is limited to Dutch operations...