All terrains are nice until you get into anything gooey or sticky. Then you're screwed...and I hate mud and don't go looking for it. When I lived in SoCal I had AT's on my truck and they did me fine. Then I came back to Michigan and on my first trail ride the wet muck just ate them alive if I wasn't constantly flooring it.
A couple years ago I bought my first set of radial mud terrains and had them siped. I'll never buy anything but muds again!
The siping makes for many times more little biting edges than the stock tread pattern had. So now you've got mud tire ability in deep and gooey stuff and very good road manors. Don't expect them to stick like Formula 1 tires but onroad they aren't bad at all. Those Mud Kings pictured got me through a winter with NO problems. Now I'm running 33" TrXus MT's on my Ranger that came with factory siping and again, they rock in all conditions. Has to be glare ice or just roads so slippery anything would slide before I get concerned, and even then I just let off the gas and I have traction again.
Muds+siping=kick ass tires
Oh yeah, Cooper makes some good shit. I've run some of their offbrand muds and lots of my friends have run Coopers. No one's had any problems with them. Great stuff for the money.