You need both. Don't trust the Florida weather forecast for December, even the day before your trip. One year, the forecast the evening before our trip was low 70s for highs all week. We got there, and that was the temperature arrival day, and then they had an unexpected heat wave and the highs were between 80 and 90 with some record highs. We had packed for 72 and we were sweltering in our jeans. Another year, we got there and it was in the 80s and we wore shorts day and night for 2 or 3 days, then a cold blast came through and by the end of the week we were in jeans, sweaters, coats and gloves all day. You absolutely never know what the weather is going to be in December and it changes really quickly. It is a pain to pack for that time of year, but you need a little of everything. We went every year in December from 2008 to 2012 and I don't think we ever had a week that had the historical averages of 70s all week. The weather can be all over the place.