Wow I could see the argument being made for Tony before Avengers(Lack of Feats for the Destroyer/Thor) but after Avengers I don't see how anyone can say Ironman wins.
Just look at the two fights between the Thor/Tony and Thor/Destroyer
Thor/Destroyer fight: Thor fought the Destroyer on a totally different level. He was smart, methodical, and didn't leave anything up to chance.
The Destroyer's beam was powerful enough to injure Asgardians as strong as Volstagg with residuals from it's blast and fists. We know for a fact Asgardians/Frost Giants are extremely durable just look at what Loki withstood in the Avengers movie. Even a thrashing from Hulk only left Loki disabled and not even KOed. The Destroyer's beam was able to seriously mess up Volstagg to where he needed assistance to be moved around. It was also heavily hinted at before Siff attacked it that a direct attack by the destroyer would have killed Volstagg while he was laying on the car.
Also Thor took no chances with that beam, and after what Thor survived in both movies I would take that as a sign of respect to the Beam and what Thor knows it can do. HE decided the best course of action was to not let that beam touch him at all and and he also decided the best course of action was to use it's own beam against itself.
Now once again before Avengers we had no real guideline with how that compared to human elements, but after Avengers we know.
Thor/Ironman Fight: Thor is obviously not trying to seriously hurt Tony cause throughout the fight we see that if Thor wanted to seriously hurt him he could have. He easily breaks IM's armor with his hands. A simple headbutt dents his armor. Everything Tony throws at Thor doesn't even hurt him even at 475% power levels for IM. We easily see Thor rip IM's face mask off at the end without even trying. IMs best attacks couldn't even get through the Leviathan's armor but we see Thor's lightning damage multiple's of the same beasts. You can also see that even though Tony absorbed Thor's lightning that where the lightning did touch it caused burn marks in IM's armor. That means to me that even though the lightning acts as a power up to IM if Thor really wanted to put Tony down with it he could have.
Also a hammer throw from Thor damages Tony and we know from the above examples that if Thor wanted to that Throw could have taken Tony's head off if he threw it as hard as he could have. Compare that to the Thor's throw against Destroyer. The initial impact from his throw only tilts its head, and it takes a surprise attack to knock it off its feat. Just for comparison when Hulk tried to catch Thor's hammer it still had enough force to carry the Hulk backwards and put him on his back same with a hit from Thor. The Destroyer only got it's head knocked backwards.
So what we have a is a none holding back Thor fighting smart and knowing it's opponents full capabilities decides the best way to take out teh Destroyer is to force it's own beam back into it's face and he doesn't even want to get hit the beam at all.
Thor's fight with Tony and Thor doesn't care at all about getting hit or taking Tony out quickly. He is more concerned with not trying to hurt Tony to badly.
Destroyer wins this and pretty easily. Ton'y flight may keep the match going for awhile until he runs out of power.