Turks and Caicos or St Kitts and Nevis? Which is a better vacation spot?

I haven't been to either, but I've researched both islands. If you don't want beaches then deffinately St. Kitts and Nevis. They have a fort, volcano, old churches, monkeys, and much more, and all the towns are on or near the coast, the whole interior if the island is wilderness, so it's not as crowded as some other islands. You can easily explore by car, and take a ferry to Nevis, which is less visited.

Not sure about nightlife, there is probably some in Basseterre. State Department Website advices not to venture out at night by yourself though, because of crime, so if you do, go with someone else, and leave any large amounts of cash or valuables in your hotel.

St. Kitts looks amazing. You will love it. It's different from most islands, because it has unique culture, landscape and history, that doesn't compare to any other island. The islands don't have the best beaches, so most people go to those islands not for beaches, but the things I mentioned above, so it is perfect for you.

I would recommend flying to St. Eustatius or Saba for one day. They're even more remote then St. Kitts and Nevis. You will truly feel alone, and find what you are looking for. Montserrat is also a good day trip option.

When you're on St. Kitts, deffinately visit the fort, Romney Manor, Basseterre, climb to the top of the volcano, and take a day trip to Nevis.

Have a nice trip.