regarding overshot, undershot and converging canines. What is considered the worst? What are the implications of these faults? And at champ shows, how many points would you lose for these faults?

In the UK dogs aren't judges on points.  Incorrect dentition is structural and the mouths that you mention are therefore all serious faults.  Extreme examples of bad dentition would impair eating, a basic requirement in any dog and therefore should not be encouraged.

undershot and inverted canines are a serious fault in staffords,overshot mouths can be corrected themselves sometimes as the head and face grows and the staffords head splits it will usually pull the jaw backwards.a friend of ours had a seriously overshot mouth  and he needed to have alot of denistry work done(not him his dog)

I would say in staffords an overshot mouth is the most forgivable of the three.

Sarah