Well life is short and you are only in that port for just a short time. I have been to all those ports except for St Kitts.
It looks like a busy cruise and you will feel like you need a vacation afterwards if you are like us when we took our first cruise. We are booked for our 27th cruise in a few months.
I would suggest you learn about each island and learn about all the excursions offered. You'll know what your interests are to help your decision.
But for St Lucia the thing for us to see there was The Pitons. There are several excursions. We chose the one that went by bus going and catamaran back. That gave us the chance to see the country side and then by sea.
Antigua has a beach for every year. So a good beach tour is nice there. But do study up on it. Enjoy yourselves and have a great cruise. Happy Anniversary.