Suzaku is, and always has been the Lawful Good paladin of the show. And his story is that of the Lawful Good paladin who is beginning to lose his grip. He is slowly being corrupted, and by the end of the show Suzaku will be a fallen paladin. I agree with you that Suzaku is Lawful Good.
However, I do not agree that Lelouch is Chaotic Evil. Lelouch's character archetype is one of the "I'll eat the forbidden fruit so that I may achieve my goal and make whomever I'm doing it for happy." The type of guy who willingly becomes evil, and knows that he is becoming evil, in order to fulfill an altruistic goal is Neutral Evil. Lelouch is without a doubt evil, as he has no qualms about killing whoever is necessary to carry out his plans, but he is notably NOT Chaotic. Chaotic aligned characters take the path of least resistance toward their goal, and more often than not for those of Chaotic Evil alignment this translate to mass slaughter until said person gets what they want.
But Lelouch is more refined than that, he crafts complicated plans and schemes to overcome boundaries, boundaries that the Chaotic Evil character would simply smash to bits without the slightest concern as to what others would think. Lelouch shows concern for things a Chaotic character wouldn't bother noticing.