I have been to Maui, Grand Cayman, and Cozumel. Maui has the best/most non-diving attractions. There are a million things to do on Maui, and a week or ten days is not enough time. The helicopter rides are very cool. You can ride a bike down the volcano. There are a million beautiful beaches, with lots of good places to surf, bodysurf, or snorkel. Driving the Road to Hana is a nice way to spend the day (if a bit touristy), but if you get an early start, you should be able to find some waterfalls that you will have to yourselves. There are white sand beaches, red sand beaches, and black sand beaches. Golf and horseback riding are also available. You can also go to a luau, which again is kind of touristy, but is a non-diving attraction your fiance may enjoy. The diving around Maui was also very good when I was there. We saw turtles, sharks and rays on virtually every dive. The whales were also in the area when we were there, and we could hear them singing during most of our dives.
Grand Cayman would be my second choice. I went to Grand Cayman for my honeymoon. We stayed at a resort on the east end of the island and did a lot of diving. The diving was outstanding, although we didn't see as many sharks and turtles as we saw in Maui. Stingray City is fun. Grand Cayman is just as expensive as Maui, but there is not nearly as much to see and do aside from diving or laying on the beach. The scenery in Maui blows away both Grand Cayman and Cozumel.
