Narratively speaking it'd be Luffy since Luffy could of used FS to tell the other Supernovas to get out of the way of Hakai, but thanks to PiS (or Luffy's general incompetence) he didn't, and therefore caused Zoro to take on Hakai, which in hindsight was just a way to make Zoro much less effective than he would of been otherwise against Kaido and to get Zoro out of the way for Luffy to fight Kaido solo.
Also Zoro's not gonna reflect on any of his or Luffy's shortcoming in this war because at this point he's a complete bum who only fights and say one liners, and as he currently see himself and Luffy, he prefers being disposable and Luffy to get all the glory and spotlight because he's Luffy's lapdog.
As for Killer he never was important as a character, but Kidd's poor decision making as a captain has indirectly cost Killer the ability to control his expression and to laugh uncontrollably. While that's fucked up, it's not like it's such a drastic character change to us as the audience because we've never really seen much of Killer until Wano. Most of what we know of Killer comes from Wano so it isn't as haunting as it could of been.
So as characters of a story I must say that while Killer's more fucked in a real world sense, Zoro got the complete shaft in terms of narrative, and since these are fictional characters, narrative has a much higher priority in my book. So I'm voting Zoro, Luffy's personal toilet.