Kenny. No question about it. Here's why.
I have to believe there's a reason we never actually see him die. Standard fiction trope-reading suggests he'll be back and I really think this would be the best possible option for season 2.
At the beginning of season 1, Lee is on his way to jail. His life is ostensibly over. Kenny, similarly, has lost everything: his wife, his son and then the only companions he had left (whether he got on with them or not). He's in a fantastic position to find a new motivation. I personally believe it should be the same motivation as Lee: Clementine.
Lets say that was Omid and Christa on the hill and Clementine met up with them, a reunion with Kenny would be ripe for drama with differences arising from whether Lee said Omid and Christa should look after Clem or Kenny should.
More potential drama: If Lee killed Duck for Kenny, then later the boy in the attic, then Clementine killed Lee... how the hell does Kenny feel about that?! The little girl in his care nutted up and did what he couldn't, killed a loved one when all hope was lost.
I think it's a win for all players too. We all have some kind of emotional attachment to Kenny: If you liked Kenny you're playing as a character you like, if you didn't like him, you play in a way that turns him into someone worthy of your approval and of Lee's (hopefully) high standard of parenting.
TELLTALE: PLEASE LET ME HAVE THIS VERSION OF THE GAME.
Please, I'd love to hear everyone's thoughts on this.