Rakshata is supposed to be a genius in her technology field. Diethard is a media master, with his superb control and foresight to act as Lelouch wants without direct orders. Todou beat KFs in the original war with conventional weapons. CC has lived for centuries, and she did save him from Cornelia and understands the extent of his schemes; though, of course, CC seems retarded by how she didn't realize Mao would be coming after her or safeguarding against Lelouch's power going berserk in an unexpected situation. Rollo is either easily swayed by sentimentalism, or is just a dumb faggot. Like others have said, Kallen is intelligent, and she's displayed it with her creative use of the Gurren arm and direct combat skill.
But of course, Lelouch is a charismatic leader with amazing tactical skill, and as such, he's the cohesive force behind the knights, eclipsing the rest, even if he isn't any smarter.