It is boring to be collecting the same head for all characters, but I guess that's what you get with the Headhunter packs. The main difference with these is the size for each class. Krieg's I think is kind of awesome. I saw a video of the upcoming skins/heads for Mercenary Day, and they at least varied the facial expressions of the snowman heads.
In case someone looks this up, to answer my own question above, the skins drop from Wattle Gobbler, who can also drop the heads.