Giorno wins. Gold Experience Requiem is even more broken than Saitama is. With GER, Giorno has the ability to automatically nullify any cause and effect, meaning that Saitama simply can not touch Giorno no matter how strong or fast Saitama is. In the JoJo light novel Giorno literally survives the end of 36 universes. It is the strongest defense in the entire JoJo franchise.

Giorno can just put Saitama in an infinite loop and leave him there for the rest of time.