Griffin is the man. I expect him to get the start as Payton starts to make his decision that he will be the #2 and only other QB they keep. I'd be surprised if this doesn't happen.
You don't necessarily start the guy you like the most. You start the guy you most need to look at. If McCown Starts, it will likely be because they really need to look at him. And Vice Versa. Either way they will both get plenty of snaps.