Spent the first few years of my life on St Maarten and have been back a few times. It's a good starter island for the Caribbean. Curacao and Barbados are my top picks. St Lucia is beautiful and good for an active/adventure seeker but is also very different from other caribbean islands because of how the island is laid out (very mountainous).
Other options I'd recommend would be Tulum in Mexico about 75 minutes south of Cancun. It's relaxing but also a lot of true Mexican culture if you like history that makes you walk/climb/swim. Or go to Liberia Costa Rica. The ecoadvanture there is great.