Looking back at the old TV magazine clips I have, the characters they pick for the week are:
Turn 12 [Love Attack] - Milly
Turn 13 [Assassin From the Past] - Shirley
Turn 14 [Geass Hunt] - V.V.
Turn 15 [The World of C] - Charles, C.C., Lelouch.
Turn 17 [The Taste of dirt] - Suzaku
Turn 17 & 18 (another mag) - Suzaku. The pic shows Suzaku & Gino but description points out "Suzaku (left)". Is it so hard to find a pic of him alone? XD
Turn 18 [2nd Tokyo Battle] - Nunnally
Turn 19 [Betrayel] - Schenizel
Turn 20 [Emperor Disqualification] - Charles
Turn 21 [Connection of Ragnarok] - Lelouch (monthly magazine), Marianne The TV Weekly).
Up to now, looks like there's a pattern of showing the character in spotlight for that episode.