I have noticed an alarming number of errors on this board, and I'm going to start trying to eliminate them so that people stop citing them as evidence for their theories.

The second one is the constant claim that the 3rd Hokage was "the god of shinobi", "the most powerful Hokage", the most powerful Kage of his time", etc, etc. This claim has virtually no evidence for it, and the evidence that Hirzen was the strongest Hokage is very bad (especially compared to Hashirama.

Hashirama is clearly stronger than Hirzen ever was
A sensible and consistent application of the evidence tells us Hashirama was clearly stronger than Hirzen. Now of course, anything could be wrong. For all we know there was a hidden leaf black ops ninja who we were never told about, who kept his true power hidden, and was actually stronger than the Sage of the 6 paths... but that's not how logic works. You don't imagine something that could be possible, you go off the evidence. Let's look at the evidence.

Evidence for Hirzen
- Some hyperbolic remarks in the manga, these being; a) that he was "said to be" the strongest ho/kage, and b) the claim he "was said to" "know all jutsu in the leaf". These 2 bits of evidence are extremely poor. The first remark is hyperbolic, and in the manga we've seen no end of remarks like this that were subsequently proven to be hyperbole. Remember how we were told Haku's jutsu had "never been stopped", or how "there's no stopping" Oro's soul transfer jutsu? You know, right before both were stopped. There are dozens of examples of this sort of hyperbole in the comic, which is why people don't go off hyperbole, they go off feats. Comic books have this problem all the time, which is why the 10 eyed man isn't actually the "most dangerous man in the world" as Batman comics hyperbolically state. Also consider the source here. This isn't a comment we're being given by the narrator, or by someone with credibility. These 2 remarks are from Iruka, some no name ninja's, and Oro is mocking that he's able to beat "you who were said to know all jutsu in the leaf". You act like the Sage of the 6 paths declared it to be so, and carved it on a mountain of truths.

As for "knowing all jutsu", he clearly doesn't know how to perform them, and if he does he was really dumb not to use them in a fight to the death with Oro. Maybe he knows of them, but it's far too much of a stretch to grant him every jutsu in the leaf with no evidence off such a flimsy remark as "he was said to" know them all (the Manga is full of these sorts of patently false remarks, just like Haku’s jutsu being unstoppable). We’re even explicitly told later that affinity with all 5 elements is impossible without the rinnegan. So at best, this reputation remark is a reference to generic jutsu… and as someone else said, if you take away bloodline abilities and elemental jutsu, does that even leave much in the way of jutsu that matter? Not really.

- Hirzen scored high in the databooks
There is no reason for us to treat the databooks seriously. They’re not written by the author, and are full of obviously ridiculous material. Ameratsu is not “as hot as the sun”, and Naruto isn’t dragonball Z, where power levels mean something. For heaven’s sake, the databook gives Oro the same Genjutsu score as Itachi (a 5), which is patently ridiculous. Nobody should be invoking the databook as evidence of anything, no more than non-cannon star wars material, or a bunch of fanfic really. The scores in the databook do not represent characters actual abilities (Itachi for instance owns Oro every which way on Genjutsu, yet has an equal score… ridiculous).

- Hirzen “beat” Oro and the 2 edo Hokages.
Oro says very clearly that the 2 hokages are toying with him, and that’s evident from reading the manga fight (remember, the anime doesn’t count), where the hokage spend most of the fight standing around and letting Oro talk, and when Oro prompts them they do a few jutsu, but basically they just stand there. There’s very little reason to believe these guys are going all out, and given that a) they’re fighting in a confined area that massively disadvantages them, and b) what we see off Hashirama’s power later, it’s pretty clear we can’t take the fight at face value.

I won’t use the invented logic of “Oro hadn’t perfected Edo Tensei”, we have no indication that means they weren’t at full strength, but they clearly aren’t being made to go all out, because Oro thought there was no way he could lose, partly because he didn’t know about the reaper death seal, which allowed Hirzen to take him by surprise and stop the fight before Oro got serious. Remember that your ability to control your own body is important to utilising your proper strength, the Hokage being mindless robots for Oro to control prevents them using the fighting genius they normally possess. Maybe the 2 Hokage would have gotten rid of the explosive tags if they could control their own movements, but Oro’s tags didn’t require them to because he knew that explosive tags couldn’t hurt them. Remember, sometimes the author has illogical things happen, then retrospectively explains them. Like when Madara “let” Onoki blast some of his armour off, just so we could see the 1st Hokage’s face.

This brings me to the next point, which a lot of people have flagged. The author changes his mind. Maybe back in volume 17 Kishi thought of Hirzen as the strongest (or 2nd strongest) Hokage ever… but it’s very obvious at this point that view has been retconned. Now we don’t strictly need to use this logic, because the above arguments I addressed don’t really give much support to the idea Hirzen is that great, but certainly it’s fair for Hirzen fans to feel like once upon a time Kishi intended for Hirzen to be one of the best Shinobi of all time. What that shouldn’t blind them to is that there’s pretty much no good evidence left to suggest he was, as we’ve gotten more and more evidence of stronger and stronger shinobi as the manga went (some who died a long time ago, some who are alive right now). I also feel like old age is a really crap excuse for Hirzen… sure, I can buy he was weaker, but Onoki (who is far older) is doing stuff that makes Hirzen look pitiful, such as carrying islands and meteors, atomising large areas, summoning giant stone golems bigger than Hirzen’s earth wall, etc. Based off feats, Hirzen probably isn’t in the top 20 shinobi, and even that’s charitable. I’m sure he had a kage level strength, much like Tsunade who gets unfairly criticized, and we should remember that Itachi and Minato show us power doesn’t require scale or flashiness. You can have relatively small and simple techniques and be awesome. But we can’t just look at some hyperbole and a fight where nobody was going all out (under special conditions) and then say “yeh, Hirzen MUST have been the best… some randoms said so”.

Evidence for Hashirama
There’s so much, I feel like there’s not a lot of point getting into it all. We’re told, balls out, that Hashi beat EMS Madara and the 9 tails fox. Then we see a double page picture of the fight, which seems to tell us that “yes, it was just him v.s the 2 of them with no help” (something we also see in that animated scene of their fight, though I think we shouldn’t give anime any weight really), and then we see Madara resurrected and are shown he’s even more awesome than we thought, and he apparently still respects and fears Hashirama (something evidenced from flashbacks too, where he’s apparently fought the dude multiple times, and lost, and can’t handle it when people mention his name; “never mention THAT shinobi’s name in my presence again!”… this is right before Madara effortlessly schools Mu and Onoki at the same time, remembering this is Mu and Onoki who have done stuff much more impressive than Hirzen, and Madara only had the EMS at this point, and it's subsequently revealed Madara wasn't even trying in this fight, and when Onoki asks him why he never tried against him and Muu, Madara just asks him if he'd really try against a child, because apparently one of the most powerful Kages ever, along with his master, are children compared to EMS Madara... the same EMS Madara who Hashirama beat WITH the 9 Tailed Fox).

Even without the Rinnegan, or Hashi’s DNA, Madara has techniques like perfect Susanoo, against which the 5 kages are helpless. And Hashirama apparently beat him with it… are you kidding? There’s no way Hirzen could have done any of this… and please remember, Madara wasn’t trying before then in his fight against the kage, so all this “Garra and Naruto nearly beat him” stuff is ridiculous… Madara wasn’t even trying then. Then look at the scale of the techniques Madara uses, which were apparently all Hashirama’s- creating and controlling whole forests (with pollen that makes you fall asleep), healing yourself without seals, having Tsunade like strength, and summoning giant wood dragons? Oh, and Hashi can use his seemingly bottomless chakra to create tonnes of wood clones, which nobody except Madara can differentiate from him, and which seem to have comparable powers to the user themselves. Yeh, good luck smelling out the real Hashirama when the air around you is filled with pollen that puts you to sleep when you inhale it. Did I mention Hashi could, at his peak, summon all the tailed beasts (remember, he controlled all the beasts at one point). Remember, every technique Yamato can do is like a pale shadow of Hashi, and Yamato is himself a pretty impressive Shinobi who summons small mountains and lakes effortlessly… again, it seems absurd Hirzen could have touched someone like this, whose hype is even better, and more decisive than Hirzens. In the 3rds case we’ve got some no name ninja’s saying “he was said” to be X good, while for Hashi we’ve got guys with cred like Madara and Kabuto saying “he was the only one who could beat me”, or “his power was so incredible, it was thought a fairy tale”. This is a guy whose blood is apparently so potent, it can do stuff like let ShiSui’s eye work once a day, instead of once per 10 years… that’s a 3650 fold increase in effectiveness… that’s how powerful a mere portion of his chakra is… indeed, it seems to be able to let Tobi use his MS a ridiculous, abusive number of times, despite the fact that he should have gone blind by this point given his overuse of MS.

All the good evidence tells us we should side with Hashi, while to support Hirzen we have to cherry pick the evidence we like, while closing our eyes to the much better evidence that counteracts it, and ignoring basic principles of logic.