The selection of best quarterback ever is doubtless a subjective one. A case can be made for a number of great quarterbacks. And then are quarterbacks like Otto Graham, Sid Luckman, Bob Waterfield, and Sammy Baugh whom I never saw play.
I do not personally like the quarterback I am going to name, and he does not have the Super Bowl rings that Tom Brady and Joe Montana have. But the best quarterback I have ever seen is Aaron Rodgers. He has good size and mobility. He certainly now has complete command of his offense. But he has a combination of fast release, velocity, and accuracy that is simply exceptional. The decision might be close to a coin-flip in some instances, but I would take him over Brady, Peyton Manning, Unitas, Elway, Montana, Steve Young, Favre, and Namath.