without doubt, Superman, unless the Flash has a few grains of Krytonite to weaken the man of steel. Superman can fly to other galaxies in a nanosecond, go back into time which takes great speed. Flash can only exist on Earth as he needs oxygen to breathe. At best for the Flash, a race would be a tie. Say there was an emergency in New York that required both to be there to fix things. They're in San Diego and takes 2 seconds (at most) for Superman to get there. Could Flash do that?
Hope that helps in your argument. Remember, the Boss is the Boss and if he/she is like most bosses I've ever had, they are always right. LOL
Former: toss up between Supergirl, Psylocke, & Wonder Woman.
To be: definitely Green Lantern. That ring gets the shaft in the comic books. They're not nearly creative enough. With a the right bat-shit crazy mind behind it, the Green Lantern ring's potential would be awesome.