I trust Gordon to save the world much more than any of the other FPS 'heroes'. If you think about it, imagine all the hell Gordon went through...and managing to survive all that he does with no prior military experience...he's a scientist! And he must be special to be chosen (well, forced actually..) by the G-Man to do his work....and Gordon saves the world.
Both Duke Nukem and Sam 'Serious' Stone are both quite ret&rded...at least Duke tries for the women (noble act), but Sam Stone.....I mean, for craps sake....Sam 'Serious' Stone...more like Serious Stoner!
...don't get me wrong, I love their games...but, no.
Master Chief and the Doom Marine fall in the same category....both soldiers, doing their duty/mission....in each case hell breaks loose (literally for the Doom Marine). They have the skills, but still....I would'nt trust my lives 150% with them....you'd think that with their skills and record of all the action they go through....I can't trust brunts.
As for Daniel Garner and Samus Aran....well, Daniel...I wouldn't. He's obssessed to finding his wife, and once he does (if he does) then that's it. He fought demons and skeletons, etc...let's see him face the whole army galore that the Doom Marine and Master Chief go through...yes, they kill alot...but, the enemies in Painkiller weren't that bad-a$$! And Samus....she stars in an amazing series of games (and stars in an amazing rendition on GC...
), but again..consider the enemies she faces....they are quite pu$$y-whipped! And I doubt she can handle much more than she does.
That's why Gordon is my choice...look at all the experience he has...fighting humans, robots, mechs, aliens, etc....i'd trust him to save the world.