Ironman vs. Thor vs. Hulk... with a twist.
The 3 Avengers have a royal rumble, all going all out and going for the kill... except we can only use their first movies to base feats off. I repeat, you can only use feats and base your arguments on the first Ironman movie (2008), the first Thor movie (2011), and the Incredible Hulk movie.
I make it this way because as has been pointed out, the power levels of the characters fluctuate a lot in the succeeding movies. So if we were to take them only as they were shown in their respective first (MCU) movies, who wins first, second and third place in an all out rumble?
Also, combatants have zero knowledge of each other.