I'd recommend Southern CA. Lot's of scenic options there....Along the coast up the PCH...And heading East through the valleys and hills into AZ. Lots of beautiful sites...but you may need a light jacket.
Average temp in Key West is 75 as a high 60 as a low. Sounds pretty good to me. The only thing is you can not beat the riding in Az! Key West in my opinion would not compare. Not unless you enjoy flat land.
We did Key West the last week of Jan. 2008. The weather below Orlando was nice. North of there was kinda chilli. We are looking at South Texas this January, but Arizona would be nice.....but far from South Georgia. How about Southern New Mexico?
I'm heading for the Keys mid-Feb. Riding out of Iowa at the first window (no snow/ice on the road, temp don't matter) around 1st of Feb. Was in Ocala area in Feb 08 and it was in the 60's most of the time and then over to Daytona just before bike week and weather was great.