Whatever you choose....just DON'T make it Bridgestone APT's....I had them on my X (stock size) and they were terribad.
For a larger tire that is under the 35" range, I can highly suggest the Nitto Terra Grappler as a great A/T tire that won't wear down quickly, practically zero road noise, and great trail and offroad performance. I run a set of 33's on my truck, and have been very happy with them. Over 10k miles on them and they still look new....
Anything 35"+ I would have different suggestions, including the BFG A/T KO which I had on my 10" lifted Chevy 1500 (35's) and they were an excellent tire. It's the stock tire that comes on the Hummer H2 (and H3 I believe)....overall great tire. Nitto's are easier on the wallet than the BFG, not to mention they have a much more aggressive tread pattern and sidewall.
I want to add that the BFG A/T KO tires....while great, are quite noisy.