Guts. - Obvious, really.
Walter. - You guys think this is a physical fight? If this is a fight about awesomeness, Walter wins. His quick-witted chemical knowledge and inevitable death makes him more dangerous than you think with preparation, and he's insanely smart. Lex Luthor could win against Superman, so Walter could win against Saito.
Segata. - Can manipulate reality, pretty much. Wins.
Jason. - Numbuh One's just a kid, Jason can overpower him and any rickety tech he makes. Also Jason has a gun. And, if needs be, an army of fangirls if he pretends to be JB. And he does an amazing impression of JB being shot.