From the standpoint of someone who lives in South Florida, I would say to decide which is more important, riding or the stops along the way? The riding from Orlando north, particularly from Ocala north, is far better than south of Orlando. Plenty of rolling two-lanes through the forest and rural areas with enough small towns and such to make it enjoyable and find gas and food. Take a look at some of the videos here to give you an idea:
http://michelmarciamotorcycletrips.com/backroad.html
I know people talk about the Keys, but IMO, the riding's not what's good about them. Sure, there are a lot of neat places to eat and drink and party, and the scenery, if you've never been there, is good, but there's also a lot of tourist traffic to contend with, affecting how much you can take in the scenery--you need to watch the road in front of you. And there's only one road for all that traffic to use.
And I suppose if you've never been here, the South Florida roads around Lake Okeechobee would seem new and different--they were when I first moved here, but now they're mostly just boring.
So I would vote for the northern part. In February, it won't be more than chilly at night--easily handled--and the days will be really nice. If you go to Miami, then I wouldn't bother with the bike. Just rent a car and then to to the Keys.