Sint Maarten
Sint Maarten is the name of the Dutch half of the island. The island as a whole as well as the French half are commonly known as St. Martin.
Both sides are interesting and beautiful but have distinctly different character. The French side is more laid-back and vaguely feels like being in Mediterranean France. There are few bigger hotels, and the speed of life is slow. The food is good, although prices are higher than on Sint Maarten.
The Sint Maarten side is bustling and has numerous large resorts and timeshares. And casinos, night clubs, bars, adult entertainment as well. The main airport is on the Dutch side, and the cruise ships dock in Phillipsburg.
The Simpson Bay Bridge is a great attraction, as the drawbridge is barely wide enough for many of the megayachts that come inside the lagoon and dock at their exclusive marinas. Occasionally things go awry, and a yacht will either hit the bridge or blow up their large fenders (which sound like a cannon when they do explode).
Or this one, where a superyacht lost control of her engine
In addition, the Princess Juliana Airport is famous for the approach and take-off fencing which attracts tourists despite the risks of getting sandblasted by Jet-A exhaust while hanging onto a fence as a big jet throttles up just a few feet away!