Dependant on conditions, but Maxxis Minnion is the best all round, use the DH-F on both front and back as its much quicker rolling than a Minnion DH-R, copes with mud well, but still quick in the dry. I'd also recommend you go for super tacky 42a compound, as the 60a is just too hard for cornering, roots and all the rest of it.
If your happy swapping tyres, then go for high rollers or ardent in the dry and swampthing in the damp, and for properly minging muddy days go for the wet screams.