St Thomas and St Maarten are both ports you can easily do on your own. We have found both to be very cruiser friendly.
In St Thomas, lots of folks take the water ferry over to St John. Some snorkel at Coki Beach or have a relaxing day in the sun at Megan's Beach.
St Maarten is a port where we just walked about town for awhile and then did a beach day right there at the dock.
We have a special needs child, so we can't do a lot of adventurous stuff.
I would suggest you get on a forum that has lots of details about each port. Send me a PM and I will recommend a couple!