In front of the pad is best. Off to the left or right.
1. you can see what you are throwing and the distance without having to get back off the pad.
2. A good distance in front at a diagonal from the pad eliminates issues where signs or posts are in the way of runups.
3. People kick the first thing they see when they throw a bad shot. I have seen tons of foot prints on signs. Location close to the tee or at the back of the pad leads to destroyed signs.
4. signs at the back of the pad are drawn on by players while they wait at back ups or for other people to throw.
5. People hang their bags on sign posts at the back of the pad not the front.
I think signs are best viewed from the pad (which means you can view them from behind the pad too)