Ditto. The 'good' dive sites at St. Maarten are often less frequently dove due to conditions...groupers is pretty far out. Proselyte reef is okay. The Bridge site was actually kind of nice - 3 or more small intentionally scuttled wrecks near a scuttled bridge structure, and some sea grass and sandy bottom and a small reef nearby. Nothing to compare with the more spectacular Saba diving, but definitely one of the better sites there. Most St Maarten diving is sandy bottom, small reef structures, mostly <70ft, at least the sites we got to. Saba by comparison is volcanic pinnacles, so not a formal 'reef' but fully encrusted with very pristine coral. It's also a tad deeper, the morning dives are usually >100fsw, although there are some very nice dives in the 50-80 foot range too.
For dive ops, I've dove with Dive Safaris (see my trip report from about 2005) the most and liked them, but I understand from another poster that Jefferson, the dive guide who was part of why I enjoyed DS so much, is now with the French's at Ocean Explorers.
I wouldn't turn down diving in St Maarten (if you're there, get wet!!) but definitely make the trip to Saba for at least a full day if you can. If you ferry over you're pretty much missing the morning dive, but if you fly over and stay overnight you can get a full 3 in even on the first day. Flights are low altitude in a de Haviland (sp?) Otter from St. Maarten. I dove with Saba Deep (Big and Little Mike, proprieters, and Little Mike's wonderful chef of a wife, Sally) and highly recommend them. Very small, personal operation.