Riddle ~ The ultimate selfless person. He wants power over others. He does not live, he avoids death. If he won the war, I think he would find that it would not get him much.
Snape ~ The jury's still out. At worst, he's the ultimate pragmatist--betraying where it suits him. At best, he did what he did because he knows something that we don't. I'm inclined to believe the latter. I don't think a world with Riddle as king would suit Snape at all.
Harry ~ Not an Objectivist hero, but no one ever said he was. He stands up for what he believes in. He fights to save his friends, no matter the cost. Some people say he's sacrificial, but I don't see it, really. He values his friends enough to not want to live without them. For a kid that spent ten years of his life utterly alone, I don't think that's an unreasonable thing. If he wanted to be sacrificial, he'd let Ginny come with them to save her happiness, even though it would kill him if she died. Of course, that's still a possibility, but I think that if he changes his mind, he'll probably find that he wants Ginny with him, and not just change it because it's what Ginny wants him to do.