I've been obsessing over this for a while haha and I have a lot to say on the matter. For the purposes of discussing my thoughts on each character I'll go in the order they're sitting (Glenn, Rosita, Daryl, Michonne, Abraham, Maggie, Rick, Sasha, Aaron, Carl, Eugene).
Glenn is an interesting debate. He is the one killed in the comics so it's unlikely they'll kill him on the show in the same way he died in the comics. The show has historically done a lot of death swaps to throw fans off. It also seems odd that Negan would tell his men to just put Glenn back in line after his outburst if he just was going to kill Glenn. At one point after Negan picks the victim, it seems like he talks directly to someone sitting on the victim's right side and there was nobody on Glenn's right. However, Glenn's become way too lucky when it comes to avoid death recently and fan's would be surprised if it was him. Not to mention his death would have a strong impact on the group because of how long he's been on the show. The most damning piece of evidence (or nail in the coffin) though is that Steven Yuen is filming a movie in Serbia right now. Flying from Georgia to Serbia is not an easy commute. It is, of course, possible that the figured out a way to work around filming schedules but supposedly production on the film and season 7 will be happening at the same time.
Rosita is probably safe. She's a minor character who hasn't been super well developed and Negan is supposed to be against killing women. I'd be super sad if she died (because we have similar personalities and I really want her character to have better storylines) but I think I'd probably be the only one. It certainly wouldn't have the major impact on the fandom that they've been teasing.
I really strongly believe that it's not Daryl. AMC pushed his death way too much, between him being shot, Norman Reedus appearing on the Talking Dead and the new show. It just seems like they're trying to make us think Daryl so we'll be shocked by the real victim. Also, this point was made in a youtube video on the subject so I can't take credit for it, but Daryl had lost a ton of blood after being shot. I mean look at him in that final scene, he's wrapped in a blanket, he looks almost as shitty as Maggie. Now ordinarily I would have no doubt that Daryl would "take it like a champ" but in that situation, there's no way he could take being hit in the head like a champ. He could barely sit on his knees.
Michonne is a super compelling theory. Obviously, she's with Rick which makes her more likely to die a horrible death. Also, there are a few POV shots in the episode before the one with the blood (they're from the people in the back of the van, so it could be Glenn, Rosita, Michonne or Daryl) however, the back of Daryl's head is visible in the POV so it can't be him. Based on where Michonne was shown to be sitting in the van I think it was probably her POV which could mean that she is the victim, as the victim was killed in a POV. But killing Michonne also violates the Negan doesn't kill women rule. It is interesting to note that the line from the comics is "He's taking like a champ" and the line from the show dropped the gender pronoun. Michonne dying would devastate the fandom and it would be interesting for this half of season six to start with the death of a love interest for Rick and end with the same thing. The POV is probably the most compelling evidence for Michonne though.
Abraham seems to be a really common guess. I don't think it's him. Apparently, the comic writer said he regretted killing him off and when he regrets doing certain things in the comics they usually don't happen in the show. Like Rick losing his hand. Also there's an exchange between Negan and Abraham where Abraham's body language basically says "Pick me" and Negan gives him a kind of knowing look. I kind of interrupted that to be Negan saying, "I don't take volunteers." or something like that. I (mostly) hate Abraham and would have no problem seeing him go but I really don't think it's him.
Maggie is who I want it to be. I can't stand her. But I really doubt that AMC has the guts to beat a pregnant woman to death on TV.
Rick and Carl are obviously safe. Negan threatens them "Anybody moves, anybody says anything, cut the boy's other eye out and feed it to his father and then we'll start." So they couldn't be the person he had chosen.
Sasha is probably not the victim. She's too petite to realistically take it like a champ and her death just isn't going to have the emotional impact on the fans that this death is supposed to bring.
Aaron is definitely one of the characters I'm leaning towards. There was a picture from a producer's (I think) instagram that showed a dummy with a cracked skull that looks a lot like him. But he's also not important enough cause too much of an emotional response and I think the show might wait to kill off another LGBT character so soon after the backlash about Denise's death.
Carl is safe.
Eugene had an emotional send off and gave Rick the bullet recipe so I'm leaning towards him as well. I think his death would have an impact on the fandom. Another piece of evidence for Eugene is that the actor who plays him said he knew who Negan killed and Chandler Riggs said he didn't. Perhaps Josh Mcdermitt knows because he is the victim.
I'm not one hundred percent sure of anyone though. I kind of shift my opinion on who it is every week. Regardless I'm super pissed about the finale ending. It was super cheap of the producers/writers to do and I'm debating not watching the show as it airs anymore and pirating it so the producers don't make a profit from me anymore. But I do enjoy watching Talking Dead and answering the trivia questions so I'll probably stick to watching it live.