With all the tire choices now, including very aggressive All Terrains to mild Mud Terrains, it seems harder than ever to make a decision.
I am in a similar dilemma. As I go up in tire size I fight the natural inclination to go more aggressive on the tread pattern. More clearance = more capable = more aggressive off road tire. I don't think that is necessarily the case though. I am currently on 33 mud terrains. My vehicle does a lot of highway miles to get to those off roading destinations. Also, I live in the west and most of the wheeling I've done tends to be in in rocks, dry dirt, sand, etc. As such it seems like I wouldn't lose anything off road by going to an aggressive all terrain, and only gain in the area of on-road (and desert) performance. Not a lot of mud, but hey, you always want to be prepared right?
For me, a strong carcass is a big requirement, with all the rocky terrain I travel on. As long as I can find a tire with a strong carcass, I would consider an aggressive AT as I go up in size. However, I'm still fighting that inclination to just go with another MT.
FWIW, here's an article that might give you some more perspective. MOAB is one of the terrains covered in the article...they recommend an MT for MOAB.
http://www.fourwheeler.com/how-to/1201-4wd-all-terrain-vs-mud-terrain-tires/
Cheers! :sombrero: