In terms of how the goats actually performed, the best would probably be Richard Hatch, since nobody thought he was actually going to win the thing, and lo and behold, he did.

As for best at being a goat, Katie didn't participate in half the challenges, did jack shit around camp, and was a bitch to everyone not named Tom and Ian. Of course, it didn't help that she was up against fucking Tom Westman, but she definitely didn't have any friends on that jury and I really don't think she did anything right other than a few parts of her FTC. She was right in that she had to rely on her social skills to get far in the game, it's just that her social skills are fucking horrible and only succeeded in wooing the two strong guys and netting her second place.