Solid. Both Big Boss and Solid Snake experienced extremely similar lives (forced to kill their mentor, betrayed by their country, soldiers who felt they had no place to be) but the difference is while Big Boss allowed his hardships to corrupt and eventually consume him, Solid Snake used them to learn from and strive to never make those mistakes again. Despite SS's assertion that he's not a hero, he's actually the only person in the whole MGS saga to maintain his morality the whole way through and do the right thing when he had every reason to follow the dark path of his father.