A lot of guys are rollin' Kenda small block or something similar. The low profile knob is good for gripping hard pack. I'm going to purchase a couple of these myself when it dries up.
I've read a review that say they aren't so good in mud but grab best on hard pack.
The other reivew winner was, I think, Rubber Queen. They said this is the best all around tire. It's good from hard pack to wet tree roots.