Controversial take...Key West sucks. Impossible to get to, terrible beaches, stupid humidity, Jimmy Buffet worship, crowded bars, etc. Why just not go to the Bahamas or St. Martin or even Aruba? I've been to Key West 3-4 times and have given it my all...and frankly, there are better options out there for my travel dollars.
I mean, I've only been there once, and it was a while ago...but yeah, the beaches suck. The town was pretty expensive, and the bar tenders just expected way too much.
It is nice, but would not be my first choice.