Two things are a must for my wife and myself.
1. Must not be too far from water, since we are canoers and kayakers
2. Must be in a climate that we know is going to stay warm.
That is why we pick Key Largo.
Any place above south Florida is liable to have frost now and then, even though the snow birds that stay up around Ocala won't admit it
Key Largo gives us access to the Everglades National Park (one hour away) and all of the Keys (the Atlantic side and the Florida Bay side)
I'll admit that I stayed in the Ocala area, I did for three years in a row, the reason, made good friends. Then, one couple bought a home on the coast, one couple quit snowbirding because husband getting up there in age and should not have been driving. We left Ocala area because of that. I must admit though, it does get cold sometimes, seen ice on the ponds with fish kills after it thawed mid mornings.
As fas as going to Miami-Key West, not for me, I was raised in Miami and would not go back on a bet! Key West? Unless one is into fishing, nothing to do down there.