Let's start this;
1. Tobi/Obito (he is just too strong)
2. Nagato (destroyed the village by himself, took Bee, Naruto and Itachi to stop him)
3. Itachi (a very talented guy at young age, his Sharingan skills were maxed out to MS)
4. Kakuzu (i choose him because he is one of the shinobi that survived a fight against Hashirama the first hokage and he has very high level ninjutsu of different natures. He has a strong physic and have 5 hearts which are attached to creatures that can move by themself, so basicly you are up against 5 enemies.
5. Kisame (although some would say he is above Kakuzu, i think it is a very close cal, because Kisame is also extremly strong, can suck chakra from the enemy and jutsu's and his jutsu can absorb the other jutsu to grow stronger. And let's not forget the insane chakra reserve. But his weakness is his sword, which adds a lot of points for his strenght, thats why i chose him at 5th place)
6. Sasori (as good as invicible, because even a puppet user like Kankuro had trouble against him, only because the puppet master Chiyo they could defeat him with a lot of effort, besides he killed the 3th Kazekage the strongest of the history of the Sand)
7. Deidara (has awsome techniques, but had taken a lot of damage with operation Gaara and the fight against Sasuke)
8. Hidan (although he is very skilled taijutsu and unique curse technique, he can't take it up against the ones above with his skills, but i don't say he is weak, beside akatsuki this man is a really high ranked ninja)