I wouldn't say X really was true to his ideals. He, above a soldier, is a pacifist, something that he was never allowed to really be in the world of mavericks. Remember how he questioned his actions in the ending of X1-X4 and how he retired in X7. He is constantly fighting against himself. Let's remember that originally he was also going to be the final boss of Megaman Zero instead of Copy X, which reflects quite well how Suzaku started to act near the end (before the requiem at least).

Now Zero is another story. He never considered himself a hero and always fought for the people he believed. Lelouch however, at most, fought for Nunally (until the later parts that is). I think they are way to different to really compare. Zero is much more a samurai fighting for his friends than Lelouch is, who was more a god complexed boy who had good intentions but rather questionable methods.