You realize that you're missing the point of the (albeit very silly) discussion, right?
The premise is "Iron Man and Batman are in the same room and have a reason to fight: who wins?" Book sales don't matter, gross earnings don't matter, it's just taking two very different descriptions of two imaginary people and talking about how they might measure up against each other if they were standing side by side.
Side discussion - Who would win in a fight between Alfred and Jarvis? My money is on Jarvis because Coulson got the best of him, and Alfred could totally kick Coulson's ass.
Side side discussion - Google fight has Batman losing to Iron Man with a score of 42.6 million to 162 million. However Bruce Wayne trounces Tony Stark with 37.9 million to a measly 11.1. Is this because Bruce has a better PR team, or was the population of Avengers Earth NY that far depleted after the last movie?
You realize that you're missing my point, right?
The discussion is who would win a FICTIONAL fight that could only happen if someone writes a FICTIONAL story to make two FICTIONAL characters fight each other. Sales, etc. don't matter in a real fight, but those factors DO matter in fiction because they can easily influence whoever is writing to determine the "winner". I am a HUGE Batman fan, so there is NO WAY he would lose to iron if I was writing the story. There are others that would have this be the opposite.
I came on here to answer the question and vote on who I think would win. I've done that, so I don't really think I've missed the point.