Fantasy Football Quarterback Help?

Aaron Rodgers is my normal starter, but he has a bye this week, so I picked up sam bradford and brett favre. I do not know who to start though. Should I start the gunslinger against the chicago bears for a chance to get somewhere between 5-20 points or do I start the rookie against the 49ers with a chance to get 10-15 points? They are both projected to get 10 points right now, Brett favre just came off a 21 point week and averages around 10 points a week, bradford came off a bye and averages about 11 points per week.