Tough to say what was the coolest lookin mini bike. I'm partial to the 10" wheeled bikes myself. Only cause I grew up on a Fox Thundebolt. Not to say I wouldn't like a nice 6" wheeled mini, a Montgomery Ward XE 525 comes to mind. But, like I said, I'm partilal to a Fox, Rupp, or Speedway. I myself might have to choose this, a 1972 Speedway Black Shadow:
Looks like a combination of a Rupp BlackWidow, and a Fox Thunderbolt.