I'd say Griffing is currently your best option as a PG, and the other two are fairly equal. They are not far behind him, though.
One thing I'd consider is a mix-and-match approach based on your opponent. Byers is significantly more dangerous on offense than the other two, but they are both way ahead of him defensively. So it might be a case of assigning Griffing / Greene to the position where the other team has their higher-scoring guard, so that Byers won't be exposed on defense.