I went to Antigua, though i'd say your destination is very much about the kind of places you want to go. My wife and i are very much sit by the pool/beach and relax first, with a bit of sight seeing. Antigua ticked those boxes for us, few things to do on the island, a few boat trips to neighboring islands, and lots of relaxing.
Another couple i know, are very active, wanting to go places, see things, so they chose to do a fly/drive tour of states, another couple did a trek in south America.
Think about the kind of things you want to do, then look for places you can do them.