We stayed at King's Kamp in Key Largo one Christmas week and we really enjoyed our stay. It is an older park with some permanent trailers and everyone was very friendly. The permanent residents came around to each site Christmas Eve evening singing Christmas carols! If you have a boat bring it-there is a boat launch right in the park.
In Key West we stayed at Boyd's on Stock Island. The sites are tight and the neighborhood is somewhat shaky but we would return if in the area. The campground is beautifully landscaped, the pool area has piped in music and there are coconuts everywhere. Grab one, write an address on it and mail it to some friends back home.