There are a few I would have to say it could possibly be:
1. The 4th hokage (minato namikaze)- because of the fact that he wasn't sealed away by the 3rd hokage, and could potentially work in madara's favour, as Naruto will surely be hard-pressed to fight a copy of his father.
2. The 3rd hokage (hiruzen Sarutobi)- come on, the old guy owned, and you know it

3. The 1st hokage (askdjnaskjdfakbfa Senju LOL idk his first name)- He wrecked madara, nuff said.
4. Orochimaru- Maybe. He would be a damn tough opponent.
5. Madara's brother- madara was always envious of how his brother was better.
6.The sage of 6 paths- could quite possibly win them the war, although i have a hunch that the sage was so strong, that even in an impure ressurection, i think would ultimately turn on madara, or, possibly on the other hand, would truly make Naruto the greatest ninja ever.
7. (I CAN'T BELIEVE NO ONE SAID THIS, but i didn't read all the pages

) The Pervy Sage who strikes fear in the hearts of men... JIRAIYA. I think this would be an epic resurrection. Seeing him talk to Naruto one more time would be extremely satisfying.
8. The 3rd Kazekage- LOL i'm just spouting ideas now

but the third kazekage was terrifyingly strong, and as a human, he would be much stronger than being controlled as a puppet.
9. A Rick Roll- That would shock anyone
10. A Pikachu- the real one-tailed beast!