Video, best?

If you're talking about companions, Motaro is the strongest because some abilities don't affect him. Shao Kahn isn't that hard to defeat.

Well, that's quite a statement. When the computer controls Shao Kahn, he becomes ridiculously fast and skilled. They even added moments where he stands and taunts his opponent (doing nothing) just to make the fight a little easier.
Actually, if you're looking for an easy but boring playthrough, Smoke is the best choice. You teleport constantly and can defeat even Shao Kahn without much effort.