Well, I'm sort-of a Florida native, and I can tell you that there is a not-very-flattering term South Floridians use for the vacation spots in northern Florida. I won't repeat it here, but let's just say its initials are RR. (some of you will surely know what I'm talking about)

In general, if you don't have kids, and are looking for peace and quiet, I would not recommend northern FL.

Tampa and Naples in the SW are perfect. White sand beaches! The Keys are a perfect secluded getaway (sometimes difficult to believe you're still in the US), although not that much of a "beach" destination, surprisingly enough. Key West is one of the few places in FL that has its own sort of cultural vibe.

What would I do in your position? My hometown bias shows: I'd stay in Ft Lauderdale. It gives you easy access to Ft Lauderdale's beach/tourist stuff, Miami nightlife (I hate South Beach, but I'm in the minority on that), small towns along the coast like Jupiter Island and Stuart, and day trips to the Keys. The Doubletree Ft Lauderdale beach has reasonable rates (although higher in peak season), great location, nice rooms, but truly atrocious service (last time, I had to call Hilton World Headquarters just to get housekeeping to clean my room -- I kid you not!).