Mechanically-speaking, the longer the lever from the fulcrum the greater the leverage.

The bottom jawbone is the lever in relation to the fulcrum (jaw hinge), making the canine jaw a Class 3 Lever.

However, with biting, there is also the consideration of the teeth meeting in a scissor bite.

Therefore, conceptually-speaking, the hardest-mouthed dogs ought to be the slightly undershot dogs (longer jaw) with a reverse-scissor bite ... and history has proven this to be true time and again.

Jack