Personally, I thought Q and A for up down (left side of BB) and I and O for left right (right side of BB) was easiest. I could've put all the keys in the middle but then you would have to control Pacman with one hand and that would be pretty hard on the faster levels.
BTW, it's I and O and not O and P because the 7100 double up the keys where as the 72xx do not.