Who did Negan kill?Watch
I would discard the women because he says 'taking it like a champion' which usually refers to boys, plus Maggie is too valuable to kill.
this still leaves 5 men, but who?
Eugene - he gave Rick the plans for making bullets. Not to mention he had a big emotional scene just before where he was saying goodbye, almost as if he was going for good. What was the point of all that if Eugene lives? Also, he got a lot of attention in the last few episodes and was acknowledged by everyone, including himself, that he was "strong" and a "survivor". That's where the "taking it like a champ" line comes in - Eugene is strong until the very end.
Glenn - lots of foreshadowing for Glenn being Lucilled: almost being hit by a bat in Terminus, picking up a baseball bat at Noah's hometown, seeing the photos of Negan's victims, Jesus looking at Glenn when Rick said "then they'd try to own us" etc. There's also been some emotional build up and character development for Glenn, like him lashing out in this scene (also cutting straight to Glenn after Negan says "this is Lucille" - perhaps another foreshadowing), as well as him killing his first man. They're also setting Maggie up to be a leader, after all she was the one that made the deal at Hilltop, and she kicked the Saviors' asses when they were captured. Either this is to remind the audience of her importance to prop up Glenn's death, or Glenn's death will push her character forward by motivating her to become stronger and raise his child.
Abraham - he gets very funny dialogue, making him a mega-fan-favourite because of his very likeable and entertaining personality. He also got a lot of attention in the past few episodes through his blossoming romance with Sasha, and earlier in the episode he expressed his desire to start and a family/make new life (in an uplifting scene where Sasha agrees with him), the tragedy being that he's about to lose his own life.
It has to be between these three characters, anyone else isn't big enough, and it's not Daryl since he's AMC's poster boy and he hasn't really gotten that much character development this season. He also has an unresolved vendetta against Dwight. He ain't done yet.
I'm picking someone random Kay?
He has narrowly escaped death quite a few times..