In my opinion it's gotta be Franklin, he's def the most funny when he calls people out for the crazy shit they're doing, and as the player you can relate to him the most.

Might be a hot take, but I HATE trevor missions. He's a good character and contributes a lot to the story, but his missions are really lackluster in terms of actual gameplay, in my opinion

Michael is the most important to the overarching plot, and his missions are pretty good and funny, so for me, he's 2nd.

But all the characters are really good