...
Why do I do this to myself?
Anyway..
I don't really look at it as there being a "strongest hokage". I do think, with the knowledge we have at this point, that the 3 that can be considered as such are Hiruzen, Hashirama and Minato. I love what Tsunade has shown against Madara, but I don't think she's on their level. Her medical skills combined with her great(though, like I stated, not on their level) power makes her a fantastic person to be a kage, but she just lacks a little too much to be put on their level.
Tobirama hasn't shown anything. We know he has an imperfect version of edo tensei, space/time ninjutsu on levels similar to that of Minato and his suiton mastery, but we haven't seen anything out of him in battle, really. His battle vs Hiruzen he didn't show very much at all.
Now that that is out of the way, the way I view Hiruzen, Minato and Hashirama is an "advantage" type of scale. I made a post in that thread I linked earlier about USSJ's hate thread on Hiruzen that I'll quote some from:
If you want to read that entire post, in response to USSJ's hate on Hiruzen, here:
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This does not mean I think Hiruzen > Hashirama, Minato > Hiruzen and Hashirama > Minato, it means I think they hold certain advantages over one another. If they were to go all out in battle, there's no telling what would happen, but just basing off what we've seen, those are the advantages I personally see.
I explained later on in that same thread the way I feel Kishi is doing the hokages:
I don't believe Kishi has a truly strongest hokage..yes, there are statements for Hiruzen saying that, but there's also statements for Minato(such as Kakashi saying Naruto is the only one who can surpass him), and Hashirama(Madara saying he's the strongest shinobi ever).
As I stated some in that post, and I'll go a little further in to in this one is that each Hokage has had a hype period. This is currently Hashirama's. We had Hiruzen's in part 1, Tsunade now in this war(she had a little in part 1, but she was mostly an unknown), Minato's not too long ago and maybe someday we'll get Tobirama, but he's been credited with edo tensei, suiton mastery and space/time ninjutsu, so I dunno, maybe that's as far as Kishi wants to go with him.
I don't believe one character's hype in regards to power > another(well..I do think Minato/Hiruzen/Hashirama > Tsunade, but that is because Tsunade isn't supposed to be about power).
So no, you're not getting what you're looking for in the sense of "proof that Hashirama > Hiruzen", but you're getting my opinion(that I think is truly Kishi's intent) that those 3 are on equal levels in power.