When I first started working out I'd grab the bar with a closed grip. Sometime after a friend of mine told me to try it with an open grip (thumb doesn't go around the bar) because it spreads the weight out a little better across your hands.

Well I started using the open grip and found it easier to stabilize the weight when I went heavy, an consequently was able to squeeze out a few extra reps.

I recently tried switching back to a closed grip but found I was doing fewer reps so went back to the open grip.

Just curious what grips other people prefer.