As a beach, Maho isn't ideal--it has large waves that crash at a rough angle and have a strong undertow.
What is great about Maho, though, is watching the planes land. This is one of the only places in the world (the only?) where an airport runway is located 20 feet away from a beach. Consequently, during the day, if you go to this beach, you can watch planes (everything from the small commuter planes from St. Barth's to huge B747s from Europe) landing and taking off. It's quite a surreal experience and makes for awesome photos.
Free parking is available at the casino next door, if you don't manage to snag a spot on the street. There are two beach bars w/ chaises and umbrellas, but it's not really worth it. Just toss your stuff on the ground, swim a bit, take some photos of planes, and hit the road.
The KLM double decker from Holland lands around noon every day, and most planes from the US will land between 12 and 2. After 2-3 pm, planes start to leave and this is an unpleasant feeling. Especially when the big ones go, there is a lot of jet blast that whirls the sand up into your face. Takeaway message: see them land (which is more interesting anyways)! Great place for kids.
If you own or manage Maho Beach, register now for free tools to enhance your listing, attract new reviews, and respond to reviewers.