Of those, I've only visited St. Lucia. There's some terrific diving in the south, near Soufriere and the Pitons. If that's were you would be going, I'd highly recommend it. If your diving would be in the north, near Castries where the cruise port is, I'd skip St. Lucia diving, as I thought the north was average at best. Another consideration is that St. Lucia has some cool things to see and do topside, so you may want to do some of those things with your wife at this stop instead of dive. When my wife and I were there a couple years ago we did a tasting at a local rum distillery, took a snorkel cruise up and down the west coast, and checked out the volcanic activity near Soufriere. You can also apparently hike to the top of the Pitons, although we didn't do that. It's a beautiful island.
James