Goodyears MTR has a pretty poor reputation here in mud, just a bit better than most AT's. Rocks, sand, etc, totally different story, probably the best all round tyre currrently available with the best sidewall.
Cooper's ST self cleans pretty well when you get a bit of wheel spin going, probably the best AT tyre I've seen in mud, but they have had issues with sidewalls, delaminating treads and tread blocks tearing. The set we had also micro cracked the side walls when fitted. Not very reassuring. We've gone with BFG AT's since. Not as good in mud, about the same in the wet, and I think the ST was slightly better on gravel roads, although the other half hasn't noticed a difference. Better milage out of the BFG's too, which surprised me.