Prophecy Girl is when it stops being so silly and has a nice payoff for watching the season, so I came real close to that. The Puppet Show was also so very close because it was a perfect blend of funny and creepy all the way through (with a nice twist), and Snyder becoming both fun and love to hate (and the ironic statement of how he wasn't going to be eaten the way Flutie was), and if I just saw the season for the first time recently then I'm sure I'd have gone with this one instead.
But I finally went with the Pack. Not so much the first half, but that ending had a lot of payoffs I liked, and can see Willow becoming more self-confident (but not yet arrogant). (And despite that Giles gets knocked out as he often is, I think his dry taunt to the wannabe hyena zookeeper hurt the zookeeper more than the club hurt Giles).