I'll leave my opinion, but that's all it is. Take it or leave it, I don't care.
First of all, unless something has changed that I am not aware of, BFG is not using kevlar in the KM2.
My short opinion is:
The MTR is better than KM2 from what I have seen. I have not run both. I run MTRs and have for a very long time. I have seen some KM2 failures on the trails I run but not any MTR failures. I don't deny there are MTR failures, and fully acknowledge the kevlar ply does not make the sidewall indestructible. However, based on what I run and what I've seen the MTR is much better in the rocks.
My long(er) opinion:
In adding to what I've written above, I am on my 4th set of GY MT/Rs. The first three were the old school tread design and I had them in 31's, 33's, and 35's. The only reason I got rid of them was to upgrade. I did try 35" TRXUS M/T's from Interco but ended up switching back to Goodyear (that is when I went to 35's). I hated the TRXUS M/T's (I won't go into the why here because its not relevent to the discussion).
I am now on 37's and have the GY MT/R's new style. Let me just say I was a big fan of the old school MT/R's as they never let me down, and the new style has been even better. They offer better traction on the rocks than before and sidewall strength still appears to be great (they claim even stronger). My 37's run great on the highway even though I have never had them balanced and I am running heavy steel beadlocks. The key to keeping them running good like that is to rotate them often in order to maintain even wear.
Now.... even though I said I have never ran KM2's, I have plenty of experience with BFG's on my other vehicles. I ran the old-school T/A KO's on both my truck and our 2nd XJ (just 30" tires). For the most part they have been great tires and even though they are all-terrains, I have wheeled with guys who have put many miles of rocky trails under these tires and they were great for what they were. Last year I switched over to the KO2's for that XJ and I think they are a much better tire than the originals. I am due for new tires on the truck and I think I'll pass on the KO2's for that because I don't need that aggressive of a tire (its a tow rig / daily driver).
So basically I am a fan of the GY MT/R's and fan of the BFG KO2's (for general offroad use). I am not a fan of the KM2's due to the couple of failures I've seen and besides that they do run small. I put my money on the tires that have (so far) never let me down and that tire is the GY MT/R. My only complaint is that they don't make a 38" or 39" in 13.50 width and their 40" is only a load range C.