Pretty obvious who leads.
What's there not to like about Lelouch? He's probably one of the better protagonists so far, neither flat nor self-righteous. In fact, his purpose for his intentions made me ponder whether he was the real villain in this right instead, and so far he certainly hasn't showed the "ZOMG l33t piloting skills" shown for a main character of a Sunrise mecha series (Yes, I'm talking about Kira Yamato).
C.C is another unconventional character. She certainly differs greatly from all 'android girl' types that come out of that typical metal shell that houses them at the start. Spunky, yet able to retain a mysterious aura around her and not to mention a pizza lover. Looking cute certainly does help too.
My last choice would be Cornelia so far. Surprising as it might be.
1) She looks hot.
2) She seemed more...human despite her earlier countenance. Despite having a hardened exterior, you can tell from recent episodes that she's actually somewhat reasonable in comparison to Clovis and soft in the inside when it comes to Euphemia. Not a typical character as well, for sure.