One word: invulnerable
Unless Goku (and I have nooooo idea who/what Goku is) is made of kryptonite, Superman (the old school "faster than a speeding bullet, more powerful than a locomotive, able to leap tall buildings with a single bound Superman") would win.
As for Optimus Prime vs Rick Hunter... I'm guessing we aren't talking about "Hunter" the television series, right? I mean, Fred Dryer was, well, robotic but I don't see him in a match with a Transformer... :lol: