With the 17" stock rim, you have two options for each tire. For the all-terrain, the LT285/70/17 and 315/70/17 (~35"). The mud-terrain has the same sizes, 285/70/17 and a 35x12.5/17. Obviously, the 285 will fit no problems, but the 35s require some trickery with the fenders. However, it can be done with just the levelling kit, several people here have done so. For my rig, I chose the 285 MTs, mainly b/c the shop actually had them. I originally wanted the ATs but at the time those tires were backordered a month. These tires are pretty popular here and BFG didn't make a whole lot of them originally, so they are getting harder to obtain in 285/70/17. They are supposedly making more, so you may have to wait a few weeks. I'm pretty happy with the MTs however, you might consider having them siped if you get a lot of snow. Check out this thread I wrote a while back.
BFG MT Snow performance + pics