I've mostly traveled up and down the west coast, which is my preference.
I vote for Longboat Key (The Colony or rent a single family home). I also love Sanibel Island and Marco Island (although my last trip to Marco was during a flood!).
So far I have not tried the panhandle. I would love to visit that area someday. It looks amazing!
As far as The Keys go, the scenery is great but the area may be just a little too laid back, at least in the summer time. Be prepared to drive many miles to get anywhere! If you are looking for totally relaxing we last stayed at the Hawks Cay Resort. The villas are quite lovely there. It's closest to Marathon. Can't say that I'm a big fan of Key West, but my bar-hopping days are long over which may have something to do with it!