I think they can both be great. Collaros' play is not an illusion, he is the real deal. He is confident, has a good arm, and what I really like is his escapability in the pocket. That is a valuable skill that you can't really teach.
I think Reilly is just really inconsistent. It's easy to blame the team he has around him, but too many times he was terrible to start a game but then great to finish, just coming up short. He's got all the skills though, just a matter of putting together 60 solid minutes of football every game.