A lot of people think they should run wider tires in the mud, thinking they need more traction so they need wider tires. In my experience narrow tires work much better, the best mud tire I have ever used is the Hutchison Alligator (it's a 2.0 or a 2.1). I'm a terrible climber but in the mud running those tires I outclimb people I have never beat before just do to the traction advantage.

A friend of mine who has been riding for 15 years in the northwest mud and whose opinion I trust told me that the Geax Blades 1.8 are even better than the Alligators.

Something I have noticed is that effective rear mud tires tend to look a lot like farm tractor tires, skinny with widely spaces angled rear lugs. Looks like somebody got smart and realized that tractor tire makers have had the past 100 years to come up with good mud tire designs.