If only 4 I would have to go with
Elway ( carried three teams to bowls and then won 2 with complete teams)
Montana ( multiple championships, first to run the WCO)
Graham ( 10 consecutive championship games!)
Bradshaw ( eww... that almost made me throw up) ( 4 SB wins)
Brady might edge him out here. Basically a toss up. Someone Morph Brady and Bradshaws faces.
If Manning gets another 2 SB win then he probably replaces the last, because of his play elevating his teams.
Criteria...Multiple championships and appearances due to QB play!
On that basis Marino, Favre, Moon, Unitas et al don't make the mount. Currently also Peyton Manning.