You know why it would be the flash.. AND why hes faster than Superman? He has done something no other speedster has ever done... Something Superman has never done in any comic cartoon or medium, and Supergirl has not even gotten close to.
He has run so fast that he became pure kinetic energy and crossed over into a dimension of momentum and speed.
His name is H'El, he's some new character introduced for the Super-family (Supman/Supergirl/Superboy, etc.). No idea how he factors into anything yet, because he hasn't done much in any of the appearances he's made in everyone's books.