St Maarten was beautiful, less crowded than St Thomas, and it had a cleaner and safer "vibe" to it. The people we interacted with were very friendly. The beaches and views were very picturesque as well.
We booked a Treetop Adventure Tour (through the ship) and enjoyed it. It was advertised as zip lining but it was more of a ropes course with some zip lining but it was still fun.
Shopping was just so-so, seems to be fine if you're after jewelry.
My overall impressions of St Thomas was that it had great, picturesque views and some nice looking beaches. We did a Sea Lion Swim at Coral World and that was great. Coral World itself didn't seem to have a great deal of stuff to do on a regular ticket but it had the sea lions, snuba, and sea trek available. The staff was very friendly.
Since the Sea Lion Swim was not a ship excursion, we booked it separately with no issues. The taxis were plentiful and it was $9 a person each way to and from Coral World (not sure if that's a good price or not).
We did not go to a beach but were given an island tour by the taxi driver. It did seem very crowded and congested in town near the port and there were the seemingly obligatory sketchy looking areas that you find on the Caribbean Islands. Though by comparison, I thought it was nicer than Ocho Rios with a safer "vibe"