St. Kitts or Nevis or both?

We'd like to see as much as possible. Is it worthwhile to take an expensive tour to Nevis, or should we stay in St. Kitts? Any recommendations? I've looked at A Day Trip to Nevis with Lunch on Royal Caribbean that includes Montpelier Plantation and Beach, the Golden Rock Plantation Hotel and Pinney Beach, but it's quite expensive. Any ideas? Thanks.

Going to Nevis means you don't see any of St. Kitts. We didn't do a day to Nevis until we had experienced St. Kitts twice.

What do you recommend in St. Kitts?

You really can't do both on the same day off a cruise ship. Recommendations would include the scenic railway, a full day island tour, a catamaran to Nevis or perhaps a trip to the beach. Nice island. Friendly folks.