Alot depends on what they family likes to do, and how much you want to drive. The keys are a long haul, but out west is twice as far.
We've done the keys twice, and spent a week there. Both trips we spent one afternoon and evening in Key West. We like the water and to fish, so we snorkled from the beach and kayaks, and did a trip on a boat out to the reefs. We also fished from out kayaks and the beach, and also did a half day shark fishing trip that was a blast. Also central FL has some great springs to paddle and explore.
We are in GA, and have not gone west, but would really like to, but with limited time, I cant justify the drive/enjoy ratio :)