1. Madara - I guess the final boss has to be the strongest
2. Nagato - A real powerhouse with the Rinnegan
3. Itachi - Only a few could beat him
4-8 Orochimaru/Sasori/Deidara/Kisame/Kakuza - They're pretty hard to rank but they're all have massive jutsu and their ultimate attacks.
9 - Konan - Not shown enough but paper jutsu can be deadly. We'll just wait to see if she gets another fight.
10 - Hidan - A one trick pony really.
Unranked - Zetsu - No way to tell his fighting method right now.