I've had to change my usual Christmas/New Year trip this year. We're thinking about sometime in the early or late spring--can't do April. We've only ever visited at Christmas. Are there any times-of-year that are better than other?
I like late April/early May. Everything is open, high season is winding down, the weather and water are usually really nice and you might catch some of Carnival. As pat stated, any time is good but some specific time periods have a little more to offer.
My wife and I like March and November. March is really good for a whole bunch of reasons. Lodging prices typically drop after February, and at some places by as much as 30 percent. March is also the driest month on St. Maarten with a average monthly rainfall of of about 1.8 inches. Daily highs are warmer than in January and February, but not as beastly hot as in July and August. About 82 degrees (28 celsius) during the day and around 73 degrees at night (or 23). And, everything is in high gear and nothing that I can think of is shut down like it is sometimes in September. Finally, hurricanes and tropical storms are not on the radar at that time of year. Hope this helps.
P.S. -- November is also nice, but it is definitely 'wetter' than it is in March. And, motel prices typically don't begin to rise until December 1st or so.