Rolf and Jonny mainly because they're so funny! Plank is also cool..Kevin used to be my favorite of the secondary characters even though I still like him he's not exactly on the top of the list anymore.

He's totally random, which is hilarious, and mostly innocent. He's nice to boot, making him the least likely to pummel someone for no good reason. His spacey, non sequitur attitude makes him the best supporting character to me.