The biggest issue with the QB competition is CBJ's resiliency factor. QBs are like thoroughbred horses. If they get spooked too early in their development, many won't recover their confidence right away. They'll start second guessing, forcing throws and making bad decisions. It will sometimes take years for them to recover and maybe even a change in teams or coaches (See Nate Peterman). QD has been under the lights. He's been hit enough to know how it feels and probably has the best chance to recover from a big mistake. JG may be one of those guys with the natural ability to snap and clear but you won't really, really know that until that first blind side sack or obvious bad read that turns into a pick 6.
Based on that, my prediction is we will see QD listed as the number one toward the end of fall camp. We may even see JG and SJ listed as 2a and 2b. QD will start against GT and I would suggest CBJ won't even evaluate him until after the Florida game (no way he will ever start of RSF against Florida again if he can help it). He'll keep the job as long as he is lighting up the scoreboard and stays healthy. JG will get playing time but will be brought along slowly so as not to spook him too early. If and when he replaces QD will be determined by QD's play and health.