It depends on the slop.
Skinny tires are great for cutting through the slop down to a more firm surface to bite on ... if there is firm stuff underneath the layer of slop.
If the layer of slop is deeper than the ground clearance of the vehicle, then you're better off with the floatation of the bigger/wider tires.
Either way - you still need the wide lug spacing of mud tires in order for the tires to eject the buildup of mud.