Alright, before you flame, the title is more to draw you in...
I have always been a huge fan of Tobirama, even when the only time we saw him was when orochi summoned him to fight Sarutobi in the Chunin exams.
what i want to know is, where do you think he stands as a chakra user?
Facts
Can created seal matrix's (like Minato) with only a touch.
Can perform the water dragon with only one hand seal.
Adapted several Jutsu to fit his needs on the fly, this is shown when he uses both Minato's and his own Seals to Teleport.
created A Kage bushin without a handseal.
When using Chakra, he can sense nearly anything, even Madara from two Countries away.
but here is where my theory gains some actual credibility.
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He took a Rasengan from Minato, Maintained the shape and power and struck Obito with it!
Im not Kishmoto, So i obviously cant back this up, but hes got to be one of the top Chakra users (Manipulator) of all time.