All of the keepers mentionioned are great it is hard to pick just 1 best keeper. They kind of get to a level where it doesent matter which one of them you have in front of your net you can be sure they are gonna make it all but impossible for the opposing side to score.
Not saying he is one of the bests but at all but I like having "old man" Keller in the net for US
Well the only reason Kahn is being speculated as being the number 1 goalie for Germany is because of his age. I'm sure all of us here on the forums know his abilities and what he has done for his nation and club.