I must admit though that although the things that were done in the mission were brutal I kind of enjoyed it all it made the game different to me. That game I think introduced a lot of new things to video games.
Everything in the game was pretty violent. But if I were to pick only one it's definitely when Trevor tortures that guy. However it's only a game, and it was a pretty cool mission indeed
When it comes to violent missions defitely the ones that involve Trevor are the most violent. Since the one with the torture's already been mentioned, probably the one when Trevor kills Johnny is probably the second most brutal.