I just can't comfortably clench a MM cob. To me, they're just too heavy on the end, so I get a lever effect, like carrying a crowbar in my teeth. I prefer straight pipes to clench. The smoke doesn't waft up into my eyes, and they just look more friendly, IMO. I find it hard to smile with a bent.
I look for pipes below 1.5oz. I also pay attention to the bit. Some just feel better than others, and the wider the bit is, the easier it is for me to hold. Narrow bits tend to give me more torque for some reason. Also, I look for smaller thickness in the chamber walls. The less weight focused on the end of the pipe, reduces that crowbar effect also.
But, I have been at this a while. I guess if you don't mind a little smoke in your face, try a bent pipe as your first clencher. It's a shame that B&Ms take such an issue with people trying out pipes in the clench before they buy them. Some will let you use a little plastic sleeve to put over the bit, so that you can try it out. YMMV depending on the B&M.
Good luck.