I won't try to rank 10 because I think it's all but impossible to compare a 70s QB to 2012 QB. The rules are so different that the numbers just aren't comparable. From memory, by decade, of players I saw play(I'm sure I'll forget someone in every group or put a guy in the wrong decade):
70s-Bradshaw, Stabler, Staubach, Tarkenton
80s-Marino, Fouts, Montana
90s-Young, Elway(begrudgingly), Aikman, Favre
00s-Mannings(both), Brady, Brees(although leaving him out wouldn't be crazy)
I couldn't really come up with a 4th in the 80s. I guess I could move Elway to the 80s but I didn't think much of him then. If I did that, I'd add Kelly to the 90s. But I won't. **** Elway and Kelly.