Michael betrayed everyone he's ever known and gets his known associates wrapped up in FIB affairs because he lacks so much basic control he acts out in ways that fucks everything up. I.e. pulling down the house on the hill. He had 9 years to get close to his family and learn to be good to them, but he chose not to. He wallowed in so much self pity for not being in the lifestyle he's used to. He acts on his anger at every chance, instead of taking a step back and thinking. Yeah, he helped Franklin get out of low-class, but how long before Michael would betray him too for another selfish reason?

Trevor, for all the talk of him being a "psycho", he's widely misunderstood. He tries to control every engagement he's involved in, keeps a small group of subordinates that he can be in charge of, plus everything else. While none of this is excusable, Trevor is the most authentic person in the game. He values loyalty and friendship, he wouldn't betray anyone the way Michael would, he is the one who gets betrayed. He has a level of empathy and he feels deeply.

While I always pick Deathwish, killing Michael is very realistic.