Both guns will stop the mountain lion - if you get a shot off. Most mountain lions hunt from ambush, so the first thing you notice might be a heavy weight on your back. On the other hand, they are notoriously shy and avoid human contact, so maybe a boom box might be better.
I used to love being able to hit hard at 1000 yards. As I get older I find hitting a mini ram at 200 yards with the 22 oddly more satisfying.