Well, I guess I will give my top 5.
1. John Elway. He gets the edge because out of most of the list, he's the only one who played in the elements and still made the list. Imagine if he had played more games in the warm weather and had HOF type recievers. He only leaned on the running game toward the end. But make no mistake, the Broncos went as far as Elway would take them.
2. Tom Brady. Like Elway, he played in a LOT of bad weather and, until Moss, had crap for recievers for the most part. Brady did benefit from a Defense that was one of the best but he also was hamstrung by a coach who wanted to play ball control and yet Brady still made the difference. In games where ball control wasn't working, Belichek would let Tom be Tom and take over the game. In a system that called for a 'Game Manager' type QB, he still managed to carve out HOF numbers.
3. Dan Marino. His quick release is what we now use as the benchmark for how a NFL QB should do it. Accurate and had an 'Elwayesque' cannon for an arm. Marino could just 'will' his team down the feild. Nothing was impossible while he was on the feild. If there ever was a QB that you had to play 61 minutes against, it was Marino.
4. Peyton Manning. You may never again see a better and more accurate down the feild pass. It's almost like an art form. Could very well be at the top of the list before it's done. Any pressure on him usually spells something ugly. But it's the ONLY thing you can remotely find to critisize him for. And I thought about it for a while. lol
5. Joe Montana. He gets dropped to 5 because he's the poster child for the term 'System QB'. Not his fault and his final years with KC weren't terrible. He played in warm weather and had Jerry Rice for a reciever. Again, not his fault but arm strength was a question and not needed as much as with the 4 above him because of the system he was in. Short passes and run after catch is where a lot of numbers come from. Still, one of the very best.
It's a fun topic and there are no right answers. I watched all of these guys play and was very familiar with them. Some of the older guys like Graham and Unitas I can't speak too much for but I agree with Zues, that the players from 30 years ago wouldn't translate very well to todays game.