You know, this poll was so difficult for me to answer, had there been an "All of them" option I would have jumped at it!
All the tribes have their own flava, but I voted for the Finians. They're the only tribe not mentioned in Slough Feg's dissertation on the tribes in that old B&W strip. When they were introduced in the "Horned God" saga they were still sketchily described but the dour Scottishness of them and the turnip references (sorry, Black Adder rules my brain) won me over.
I have to say that, considering how little of the non-Sessair tribes was revealed in the Slaine comics, Ian S. did a fantastic job establishing them all in the game. 8)