The most fun sign is the person who makes me laugh. LOL
How can I judge otherwise?
I like intellectuals with a sense of humour and it is a rare commodity. Here on hub pages, I only read one hub so far, that made me laugh from line one to the end. Most of the stuff I find boring and I think it is a fair assumption that all 12 or 13 contribute to this boredom in the equal measure.
I don't think an astrological sign can determine "the most fun" part.
Compatibility is an issue, however.