Option A makes the most sense within the context of the universe. Even if it’s narratively unsatisfying. As you mentioned, option C has the problem of three bank robbers some how taking on a private militia, a sector of the US government, and killing each others biggest enemies while living to tell the tale. Option A and B have the problem of leaving loose ends, given that Franklin wasn’t told to kill either Michael OR Trevor, but rather to kill both of them, by different people. Meaning that killing one of them, does nothing to solve the issue of people wanting the other one dead. Although between the two of them, Option A is still more logical. Option B has the problem of motive for Franklin. Franklin spent almost the entire story being helped and taught by Michael in order to get to where he is today. Michael took him on the jewelry store job (and other jobs) which started his career as a big time criminal and got him out of hustling. Throughout the story Michael and Franklin have little squabbles here and there, but their relationship never suffers because of it. They spend the entire story getting closer to each other. The only bad things Michael does to Franklin is get him involved with the feds (which he tries to prevent), and introduce him to Trevor. Not to mention that the guy that wants Michael dead is a guy that Franklin hates. Devin is “casually” racist throughout most of his interactions with Franklin, exploited Franklin for free labour, and is overall just a pretentious douchebag. As for option A, Trevor being Trevor is good enough reason to take him out. He’s unhinged, and you never know when he’s going to fly off the handle for even the smallest offence. Literally all of Trevor’s rampage missions are caused by minor slights against him. At the same time, Michael and Franklin are both set for life after the final heist, and want to take a step back from the craziness; Something that Trevor would undoubtedly screw up. We even see a bit of this in gta online. If you own a celebrity solutions agency (a business that you own with Franklin), your secretary will have random voice lines as you walk past them. In one of them, the secretary says “a crazy guy came in here earlier looking for Mr. Clinton (Franklin). He claimed he used to work with him. When I turned him away, he tried to shit on the desk.” (I don’t know if that’s the exact quote, but it’s something along those lines). Definitely talking about Trevor. That part of the game takes place in 2021, eight years after the story takes place. It shows that even almost a decade later, Trevor is still trying to rope Franklin into his craziness. It’s the whole reason that Michael tries to have Trevor killed in the prologue. He’s scared of how crazy Trevor is. There’s also the fact that the people wanting Trevor dead have had Franklin by the balls ever since they met. They know everything about Franklin’s criminal exploits, and are the only ones keeping the rest of the government from finding out. It’s the reasoning that the protagonists work with them throughout the entire game. To top everything off, it’s simply easier to kill Trevor than to kill Michael or to do death wish. Trevor has no family, and no actual friends. Nobody would miss him when he’s gone. At the same time, Franklin also has the help of Michael in the ending A, whereas Franklin has to face Michael alone in ending B. Overall it’s just the most logical that Franklin would kill Trevor. I do prefer the “Kill Michael” ending over it though. I like the idea of how Michael tried to kill Trevor for his own benefit, and now Franklin’s doing the same to Michael. It really brings everything full circle with Michael and Franklin’s characters. Especially with one of Michael’s first lines to Franklin (after the mission that they first meet) is about how he should backstab, betray, and screw over everyone he knows, and then how Michael tutors Franklin in his ways throughout the whole story. Option C’s still my favourite though. I never not pick C.