1) Like any Iron Man / Steel thread (which has either of the two), it all comes down to the type of armor used. That is EXTREMELY key in any bout that includes any one of those characters. For instance, Tony wearing his first armor wouldn't last long against any modern threat, while wearing his more recent armors (particularly the Extremis) he can face threats that would earn him automatic membership in the JLA. Once again ...armor type is a SERIOUS consideration, and one that is not mentioned on this thread.2) The other component, which is also related to armor type, is whether (per KMC rules) they are at their best. The best armor (IMO) for Tony would be the Extremis (some may argue that there are more powerful armors, but I say that those are one-dimensional .....the Extremis on the other hand is omni-dimensional, giving very powerful abilities in ALL areas). However, what is the best armor for Steel .....well, obviously, the AEGIS ENTROPY.
3) The next step is for people to read up on the Entropis armor (hopefully people here do read IronMan ....I think the poster Tony Stark is a fan-boy, but in his defense at least he is current on Iron Man).
4) Then after that read up on the AEGIS ENTROPY armor that Steel wore. In the 'older days' no one would ever match Iron Man against Steel, because many of the posters then knew just what the Aegis Entropy was capable of ...and what the extremis was capable of. However, many posters for the lst 6 months are new, and they generally oscillate around their favorite characters ....meaning they only know of the Extremis, but know nothing of the AEGIS ENTROPY (probably all they think of Steel is that he is some black dude with a large hammer and a metal suit).
5) Now, here is where the meat is ....and why fanboys, no matter how knowledgeable about a particular character, always give skewed viewpoints. E.g. ....someone may know that Stark's Extremis armor is UBER powerful, but they know nothing about the AEGIS ENTROPY. Thus, they automatically say Stark wins, without knowing a THING about the AEGIS. It is equivalent to knowing EVERYTHING about SPiderman, and thus knowing about his strength, speed, agility, warning sense, webbing, etc etc etc (even where he went to kindergarten in the comics). But knowing NOTHING about Superman. And thus, in a thread saying 'spiderman vs superman,' automatically saying that Spiderman wins, because that is all you know.
CONCLUSION:
There is NO armor that has ever been in Stark's collection (be it in the past or the present, or even the one-off 'special' variants) that comes close to the AEGIS ENTROPY in any way, means or manner.
Not even close.
Now, this thread did not specify what armor was being worn by either contender (and several of Tony's armors could mess up Steel's old armor ....and for that matter it did not even mention what Steel we were talking about, because pop's retired and his daughter took over), but if we are talking about the best of each, giving Tony Extremis and John AEGIS ENTROPY, then this is not a fight.
It is a beating.
10/10 John Henry Irons in the AEGIS ENTROPY.
And it would be a quick beating ......and Tony's warning sense would simply be blaring at him that he is about to be erased from existence.
ADDENDUM:
When debating characters, it is always best to also look at the OTHER cat. Just because your character is super-powerful, doesn't mean that he is doing jack if the other cat is basically handling universal threats. If you have an armor that you think might be able to face off against the Hulk, Storm and Thor ...and give the wearer a good shot, and the other guy has an armor that is powered by entropy, a fusion of 4th world technology with an Imperiex probe shell, can stand up against Branian 13, Imperiex and warworld, can bend space and time, and has a level of malevolent destructive capability ....at that point one needs to put down their fan-boy hat, go back to the study desk, and reconsider whether saying 'Stark wins' to every thread concerning Iron Man is really a prudent thing to do.
Because, the best armor worn by Stark has nothing on the best armor worn by Irons.
Not even close ....one armored finger on the AEGIS ENTROPY has more power than all of Stark's armors (including Extremis) combined.
Put it this way ....the only armor that would have a very good chance of defeating the AEGIS ENTROPY is the Asgardian Destroyer armor. They are both powered by obscenely powerful founts of power, and they are more than 'mere' suits of armor.