The best tyres I have ever used in muddy conditions is Michelins WildGripper CompS (with Silicium)
They clear mud faster than a mud clearing thing.
Bewarned though. They are not the easiest tyres to ride on wet root or rock but in mud there is nothing touches them.
Hutchinson's Alligator is the next best thing IMO.

Mud specific tyres are a marketing gimmick IMO. They tend toclogg anyway and because the blocksare depper they hold more mud making the tyre heavier nd you just get bogged down.