I dunno Franklin was probably the most decent one. He was just raised in the hood...the hood is all he knew, as I see it. I'm from Chicago and so I can kind of relate to Franklin. He was kind of a victim of his peers and family.
Trevor is cartoonish though. Entertaining for sure. He also, though was at his core, a victim of his environment. His environment created a monster. If you look around Los Santos, everybody they meet is fucked up in one way or another. Even Lazlo hosting his new show was fucked up. Michael and his entire family had issues.
Even then, Trevor still were able to show some form of humanity throughout the story. Trevor actually cared about a woman he met...who was obviously married but still, you get the sense that he'd do anything for her. In his own fucked up way Trevor was capable of love and sacrifice for the benefit of another person. So no, I can't agree he's the worst character ever made.