I'm sure there's arguments for either style in certain circumstances. However, my default position is balls of the feet in the stirrups. This allows you to a) slip the foot out quickly in case you want to dismount for safety b) greatly reduce the chance of the foot inadvertently slipping through the stirrup and c (and I think most importantly)) stretch your leg down which helps maintain a proper position - the better you can keep your position centered to the horse's movement, no matter what the horse is doing, the better you stay on and keep control (I'll see Baxter Black's quote with the old expression 'head up, heels down').
By the way, I think the one way stop is a very useful tool and it doesn't hurt to have a helmet at the ready if you think one is called for.
Last edited by Chevaux; 07-20-2013 at 02:02 PM.