Vault Dweller & Chosen One saved the entire (Fallout)World on separate occations.... The Lone Wanderer and even The Courier's achevements are... well... more "Local".
Single-handedly obstructing a (second) Mass Extinction can't really be beat.
If The Vault Dweller failed; everyone died.
If The Chosen One failed; everyone died.
If The Lone Wanderer failed (or turned "Evil"); everyone (in the DC area) got a little sick....(?)
If The Courier didn't interfere; Caeser would conquer the Mojave with maximum bloodshed. (nothing more, nothing less)
(And if The Vault Dweller failed; The Chosen One woudn't have been born and the world would have died three times in all)
So for saving the world once directly and once by proxy; We can conclude that The Wault Dweller is the ultimate Fallout Hero, and would therefor kick the others butts. ;D