It's not entirely clear which GTA 5 ending is the best. You either kill trevor and michael or team up with them to kill off threats

1.Killing Trevor

If players follow Haines' request to kill Trevor, Franklin arranges a meeting with him. They begin discussing recent events, and Franklin (perhaps looking to justify his choice to carry out Haines' wishes) says Trevor's wildness will get him and Michael killed. He pulls a gun on Trevor, but Trevor escapes in his truck. Michael arrives to help during the chase, ramming Trevor's truck into an oil tank. Injured, Trevor falls into the pooling oil and berates Franklin and Micheal for betraying him. Either Franklin or Michael then shoots at Trevor, igniting the oil and burning him alive. Michael rants about Trevor's shortcomings, then he and Franklin agree that, "Surviving is winning, [...] whatever it takes." The GTA 5 Union Depository heist's earnings are split between the two of them.

2.Killing Michael
Things begin similarly if the player chooses to kill Michael, with Franklin arranging a meeting between the two. Michael gets off a call with his wife, celebrating the fact that he has money and his family back, but Franklin begins to explain his reasoning for what he's about to do to Michael. He says, "We both know this [...] ain't over," meaning they won't be able to get away with the heist if they don't appease Haines and Weston. Michael escapes to the Palmer-Taylor Power Station, and Franklin chases him down.

Knowing Michael betrayed Trevor in the past, Franklin explains he felt used by Michael and like he could be betrayed any day, since "People don't [...] change." Michael then says, "You did! You! Two-bit gangster gone three-bit," meaning Franklin has gone from a simple thug to a full-on, scheming and backstabbing criminal. After Franklin pushes Michael over the side of a tower, players have the option of dropping or saving him. Even if they choose save, he'll headbutt Franklin, forcing him to drop Michael to his death. Franklin then calls GTA 5's Lamar Davis, an old close friend of his, as he walks away.



watch below below how franklin kills trevor and then michael


https://www.youtube.com/watch?v=x8m417qu6BE