I feel like it could be any of them. Too many factors are at work and we haven't been given the full picture. Let's see...
Camilla: unlikely. Her death means her resurrection in most scenarios and the certain death of her killer not moments before. I'm sure there are ways for Benjamin to devise she kill herself, but he hasn't yet done so, as far as we know, and then there's her Nen Beast as a potential threat. There is no telling what it might do.
Fuugetsu: with the focus off of her for now, and Kacho dying not long ago, I feel like either Fuu will indeed go next, or the focus will shift significantly. Fuugetsu isn't going to participate actively in the war, and I doubt Melody would cooperate to that extent, since doing so inevitably means fighting other Hunters, specifically Kurapika. While it's definitely 50/50, I'd assume for now that it is not Fuugetsu. If Kacho's nen beast were not present, then absolutely, but not yet.
Benjamin: important and currently the most active player in the war, so far. Incredibly powerful, intelligent and well armed in every way. Either he goes down against Halkenburg soon, or I assume he remains a driving force. My belief is that he must live for a while yet. Without him, his soldier assassins lose real value in fighting and dying. Suicidal attacks would make sense for them to an extent, but will they really choose to end Kakin's royal line completely? Are they not patrioic Kakinites? But I could see his chances leaning more toward dying than most of the others, if only because of Halkenburg.
Halkenburg: Same place as with Benjamin. He's on the move, and he intends to win. Either there will be a clash soon, or he will play the game more efficiently. How he moves changes the entire dynamics of the war. I would assume he lives for a while yet. He won't be the next to go. But if there is a confrontation between him and Benjamin, I would assume he will win and Ben is the next to die, definitely. But not Halkenburg. Too much focus was put on him from the very start for him to just kick the bucket without good plot reason, and so far there isn't a concrete death flag, that I've seen, anyway.
Wobbl: will be future Queen/King of Kakin. I just don't see Togashi-sensei killing her next. Or at all. Certainly not with the banquet set-up. If he was going to do it or be allowed to get away with infanticide in his manga, something tells me he'd have done it early in the war.
Marayam: Considering the night perfect fortress that his room has now become, with excellent pro hunters guarding him, I just don't know how in the world he's going to be killed, at all. It's not in the works right now, unless the set-up has been brilliantly laid. Which... Togashi could do.
Tsubeppa: is it a her or a him? I hope for a he, because poor Tsubeppa is ugly as can be. And also underutilized. But he's also in league or trying to be in league with the 4th. His survival rating is quite honestly low, as is the usefulness of his nen beast. For purposes of the plot, what good is he, really? Not too much. An expendable, if interesting person.
Zhan Lei: I am biased here.
His guardian beast is my favorite. And he is my favorite Prince next to Halkenburg and Fuugetsu. As an actual monarch, I feel he's a good candidate, and would have hoped for him to reign, were it not for the dark confirmation that there can be only one.
So, I can imagine him dying some time in the future. But it seems like he's being ignored a little too much. I do recall that he gave up some guards to Kurapika. I imagine he could be pretty easy to assassinate, assuming his Nen Beast's coins aren't overpowered or super-convenient.
Tyson: Is all about
all the time. Her Beast looks like it might just be able to convert large numbers to her religion, but it is really like what others have said, she is a female Sale-Sale. She therefore has a chance of dying at just about any time.
Tserriednich: It would simply be a total
moment if he died at the banquet. And it would likely be somewhat anticlimactic for a lot of readers. The buildup for this guy is real. He will be final villain, and is least likely to die.
Luzurus: he has ties to the mafia, and I could see an assassin or careless spider getting to him and just offing the poor man for no good reason. But something tells me his involvement with the mafia, along with Tserriednich and Zhang Lei, will have a dynamic all its own in coming chapters. Togashi seems to be increasing the pace, so it is likely that some plot points will either be significantly condensed or dropped entirely. Could likely be that characters who were supposed to receive development will not get any attention, especially people doomed to die.
Right now, the most active seem like the most likely to end up dead, given recent events. This would mean Benjamin, Halkenburg and Tserriednich in terms of activity and relevant screen time in recent chapters. I discount Fuugetsu because it feels like her "arc" has ended. She will likely get another set of chapters to herself before she's done in.
My personal prediction: someone is going to find out about the ritual machine and how it relates to the ceremony jar. Then, Kurapika and other major characters will resolve the war by destroying it. I assume most of the "innocent" princes will live to see that day, namely Marayam and Woble, seeing as they are children, but Fuugetsu might manage to stay alive long enough as well.
Given how the banquet appears to be a catalyst for the second act's finale, it could be the Princes will die in swift succession. In which case, the least used will go first. Sale-Sale went, and now that leaves Tyson, Luzurus and Tsubeppa as an inactive group, a mirror to the active category. My bet's on this when I sit here typing. One of the meaningless characters has to go sometime soon, while their deaths will still mean something for hype. If Halkenburg or another big player goes, the rest of the minor princes dying will feel like so much cleanup.
I do agree with most of the ratings, and I especially liked Tser's description as a "childish airhead with a knack for murder, but his talent is scary", that's his exact portrait ^^
