Genjutu also wouldn't work with three Admirals helping each other with access to CoO, unless the jutsu can be cast on each one simultaneously. It really depends on how good his Genjutsu was. I don't really recall it being that impressive or useful for anybody outside Itachi, who was overpowered with it.
Madara would have an advantage and low-diff any 1 Admiral. Akainu probably would be hardest to overcome, as we've seen he has yet unexplained powers that defy even Haki/Logia interactions. There's no telling what that ability can do. Maybe he could even tank amaterasu and just... regenerate. They can do that, Logia, regenerate. So they have healing where Madara doesn't. And their intangibility would likely steal the win for them straight up. Madara would be too surprised and would react too late before getting hit with a three-way.
I mean, Zehahahah! Even the old man (Whitebeard) was expecting it from Kuzan, and he STILL got surprised and his spear frozen, and him almost with it! Logia hax is no joke...
Not to mention these guys are all at least decent strategists. Wouldn't be hard to team up and fight him like the 5 Kage did. Only in this case Madara would not have access to Hashirama's overpowered abilities or Edo Tensei to deal with them.
And Haki. Advanced Haki would murder Madara. But only if he didn't Genjutu or use some kind of Rinnegan power. Rinnegan is what throws it. The real question for me is: Can Rinnegan absorb the admirals themselves? Because if so it's instant-win for Madara! And if it can at least absorb Haki, it's still an low-difficulty fight for him.
I voted Madara at first, but then changed it again to Admirals. I forgot Aoikiji. There is no way a more or less normal man is going to survive getting frozen solid. His fate would be Diamond Jozu's. With broken limbs.
Remember, 1 arm. 1 hand. Hell, several fingers frostbitten or burnt. That's all it takes and he can't form seals no more like he could. Zehahahah! Or did he have access to 1 hand sealing or Sharingan doing it for him?
Susanoo would not work. It is durable, sure, but not on the scale to stop Akainu and Aoikiji. Aoijiki might be able to make it brittle enough. Akainu would just melt the ground and cause it to sink. We know it can be melted... Kizaru's kick is one of those hax things whereby it HAS to be nerfed or he instant-kills everybody. But I'd see it as fair to nerf him given Madara has no means of countering Kizaru's element. He'd just turn it into a stamina fight. And then there are those AoE attacks. If they even have an inkling from CoO, they will just unleash their own Elemental style Buster Call and that be the end of it, since meteors got low-diffed by the likes of Law, Doffy and Fujitora. No way are several asteroids going to do anything but hurt Madara's visibility, which won't bother CoO practitioners.
So again, it all depends on how the powers interact. Rinnegan absorption is scary. And if Madara has the ability to rip out souls... like Pain did, well... uh... not sure if Haki blocks that. Maybe CoC? We know Soul Pocus from Big Mom didn't affect Jinbei. I could see work-arounds. But really, access to Rinnegan is just what makes it all so muddled.
I will say that Madara pre-Rinnegan (which he activated ONLY after receiving Hashirama's cells, so technically this debate requires he have Hashirama's powers, if we insist on him having Rinnegan. Otherwise, It's all pre-Rinnegan Madara. And Pre-Rinnegan Madara will go the same way just about everybody but Whitebeard has gone when facing the Three Admirals.)