madara.
obito
itachi
minato
orochimaru
shikimaru
some people will give their judgement depending upon whether a shinobi has a kekke-genkai or not.. i am taking this into consideration in making my analysis. i think obito should be on the top due to the following reasons-
1) in a time span of 1 year( the time span i am not sure) he graduated from a chuunin to a super kage level--- he was strong enough to take on minato, who was strongest at the time.
2) minato could barely defeat him, by his own admission. he referred to obito as a harbinger of disaster and came to the conclusion that the kyuubi's chakra control is the minimum requirement to defeat him.
3) obito could also see through every action that minato took(minato said this himself). it was thought that the sharingan cant see follow the yellow flash's speed and reflexes.
4) obito is the only living individual besides madara to summon kyuubi.. moreover he did that with onlt 3 tomae sharingan whereas madara had to control it using MS/EMS. in fact, he controlled kyuubi from the belly of kushina, as the sharingan's tomae had already appeared on kyubi's eyes by then.
5) can anyone tell me how obito could slip through and enter madara's subterranean chamber with an imperfect sharingan after his supposed 'death'? it implies only one thing- that he could ue ST techniques using 2 tomae sharingan.
6) he controlled the 4th mizukage, a perfect jinchuriki.
7)he is a master strategist and manupulator. his intelligence is of the highest level.
8) his physical strength is awesome and his speed has become so great that not even naruto, even in his perfect kyuubi mode, could keep up with him.
9)his teleportation jutsu is the best. breaking into any barrier is child's play for him. he even broke into minato's barrier.
10) and last but not the least, his kamui is one of the most fearsome techniques. he can use it in conjugation with fire element, wood element, not to mention the use of weapons stored in the pocket dimension.
NB: madara should come below obito. i agree with the rest of the list