Proof: The first four hokage are the strongest shinobi

[Gaara Of The Death]

Nah the first 3 Kages are the strongest.

 

[Penguin]

I think Hiruzen, Tobirama, Minato, and Hashirama are all top fifteen or better. The rest of the hokage do not excel in one on one combat.

 

[USSJ Future Trunks]

kabuto w/edo tensei army
juubito
current madara (stomped two kages, and nine bijuu)
sage of six paths
oro with edo immortal revived hokages.

also some of those feats were done when they were oro's puppet edos.

 

[Natsu Shazneel]

Naruto should be up there as well.