Most well rounded?

[Hokage Sharingan Kakashi]

Kakashi.
He's capable of battling any shinobi in any justu style(tai,nin,gen) and with his four different elements he makes quite a formidable opponent to almost any.

 

[Megan Terumi]

kakashi, jiraiya, orochimaru, mei, hebi Sasuke before he started using MS

 

[Myogen]

Tobi, he's got Rinnegan, Sharingan, and Bijuu. Or Madara with Rinnegan, Mokuton, and Sharingan.