Who worked/trained harder to you out of three characters?

[Aznkidd]

Sorry but Sakura was developing a S-Rank Seal even though she had no a KKG or Tailed Beast.
Naruto had a head start because of his lineage and tailed beast while Sakura got here from pure training no handed power-ups.

A lineage with no one there to teach him about their lineage.
A tailed beast that prey on every second to burst out.
He is indeed lucky.

 

[DHOH]

Probably lee.

 

[Xāvî1]

I will say lee cos he is a training freak!