Depends on what each have in them.
Obviously the Sb has all the latest and greatest go fast parts. But for the fly a booster bolt and str ram would make it comperable. Personaly unless its a really cool looking sb I'd go with the fly. I like how the fly look.
"There he goes. One of God's own prototypes. A high-powered mutant of some kind never even considered for mass production. Too weird to live, and too rare to die." -Hunter S. Thompson