I've ran the km1's (x2 sets) and the bighorns, both in 35x12.50r15's, and I liked them both. The bfg's I wheeled a lot more on, mostly mud and wooded trails, and they did great IMO. For a more mild mt anyways. The bighorns did about the same offroad, if not a little better. I didn't have them long (sold the rig) but I would get them again. The maxxis were quite a bit louder on the roads if that makes a difference to you.
Sounds like the bfg's your lookin at are the rubicon take offs. If that's correct, I wouldn't worry much about not finding them in the future. They will be around as long as they are a factory option tire. Slightly diff tread than the actual km1's but they call them the same. If your on the roads more, I'd go bfg. More of a wheeler, go for the maxxis!
slate 94 zj, 4.0, 46RE, 242, lp30/35, 3.73's, 3.5 RC/IRO, 255/75r17 Rubi BFG's on Moab 17's.