I think everyone has their own semantics when it comes to things like "all-time" or "top 10". To some it's the number of championships (and/or Superb Owls). To others, it may be based on pure stats. And on and on.
And nobody's really right or wrong.
Personally, my list would always start with the QBs from the 1950's - 1960's. The true field generals that had to call their own plays.
And that's likely selling QBs from previous generations (Herber and Isbell) short.
But Starr and Unitas were the generation I grew up with, and I learned some history from the ones who preceded them or were closer to the end of their careers, so they will always be the greatest to me.