All of the beaches are uncrowded this time of year, except for Trunk, which is where the cruise lines bring their STJ shore excursions. Even Trunk is not overly crowded. Good beaches that don't require a hike:

Maho
Francis
Cinnamon
Trunk
Hawksnest
Haulover
the Lameshurs
Hurricane Hole (mangrove snorkeling)

Hello,

You could try:
Jumbie (limited off the road parking, short walk down steps/path).
Maho Bay (easy access, often sparcely populated, road side parking)
Hawknest (weekdays in the afternoon are nice for a relaxing swim with just a few other people; parking lot available)
Lameshur Bay

--Islander

"Hurricane Hole (mangrove snorkeling)"

Mangrove snorkeling? I've never thought about snorkeling in Hurricane Hole before, but now I'm curious: what do you see snorkeling around mangroves that's different than on the fringing reefs?

Hawks nest is one of the best.