Well, I can't say that I have a favorite "vermin" type when it comes to, well, anything. With animals in general, it's dogs, but most "normal" animals aren't in play very often when it comes to D&D. Horses, I suppose, and the occasional mule. So, I'm going to bend this one a little bit and pick my favorite Magical Beast, because that's kind of on the animal line.
My favorite magical beast is the Cockatrice.
