The final Cylon is somebody from the 1st season, and generally believed to be somebody from the pilot episode. (That technically includes Zak though perhaps not Joseph.)

Favourite choices not in the picture are Gaeta and Dualla. Gaeta’s been a top fan choice for some time. Dualla also has clues but would be a boring choice. Zak has gotten onto people’s radar screens because of the conversation with Lee and Bill about Zak being a Cylon.

Among those in the picture, my choice is Baltar, but there are fans of Lee, Bill and Laura — and of course Starbuck.

It needs to be somebody who is still in shadow and hungering for redemption, but will only find it in great pain.