Once you start comparing Brady and Manning to players in different eras, well, then it gets really tricky. But that won't stop us from asking the question.
Albert Breer of NFL.com wrote a fantastic piece Thursday looking deeper at how Brady got to this point, what makes him unique and his place in history.
"I think that Tommy, with all due respect, is better than Joe Montana," Patriots owner Robert Kraft said. "I know that's a leap, but I really think he might already be the best of all time. I watch how involved he is, how driven he is. He's like (Bill) Belichick, he's into the details. And he's got a skill that makes him so special, he can process all of it so quickly. ... And then, he's just got that quality. Certain people have that sincerity. He's a very genuine guy. People can relate to him. People can trust him."
Then again, Kraft isn't exactly an unbiased observer.
"He's like a fifth son to me. He's special," Kraft said.
Brady is 35 years old, an age when quarterbacks tend to slow down. Quickly. Brady's father believes that his son wants to play another six to eight years. Brady certainly sounds like he enjoys the process and the competition more than he ever has.
Is Brady the best of all-time? Let's see what else he -- and Manning -- have left before answering that one.