WARNING: Before you go any further, this post will have MASSIVE SPOILERS about both Avengers: Endgame and the third episode of the eighth season of Game of Thrones.
The weekend has ended, and both Arya Stark and Tony Stark have saved the world single-handedly—Tony by donning the Infinity Gauntlet and snapping Thanos and his minions out of existence, and Arya by knifing the Night King in the belly, and causing his army to disintegrate into shards of ice.
All of this raises the question: In a desperate bid to save all of humanity, which Stark would you rather have on your side, Arya or Tony?
Who saved more lives?
In Avengers: Endgame, Thanos first wipes out half of all life on Earth (and elsewhere throughout the universe), but because of the Avengers' persnicketiness, then decides to wipe out everyone. In Game of Thrones, the Night King looks to wipe out everyone, too. However, the population of Westeros (and Essos) is arguably much smaller than that of the MCU.
Winner: Tony Stark. Numerically, he saves a lot more people.
Who's the better fighter?
Apart from some boxing lessons and Wing Chun, the MCU's Tony Stark appears to have little formal training when it comes to the martial arts. Arya, however, has benefitted from the tutelage of Syrio Forel, the First Sword of Braavos, and Jaqen H'ghar of the Faceless Men. Meanwhile, Tony has the benefit of the Iron Man suit, while Arya has only her wits and Needle (and a nice little Valryian steel dagger).
Winner: Arya. She does more with less.
Who can take a better beating?
As Sylvester Stallone says in Creed,"It ain't about how hard you can hit. It's about how hard you can get hit and keep moving forward." Both Arya and Tony get the crap kicked out of them multiple times through the course of the MCU and GoT, but let's focus on major injuries: Tony has been blasted with shrapnel (from his own bomb), had a planet thrown at him and stabbed — again, with his own weapon. Arya was blinded and stabbed multiple times, nearly to death, by the Waif.
Winner: Tony. He's survived many more internal injuries.
Who had the tougher opponent?
The Mad Titan can fight off a number of superheroes single-handedly — it takes a severe walloping by Tony Stark to even scratch Thanos' face — but the Night King can raise the dead to fight for him, is impervious to dragon fire, and can be killed only with a specialty blade.
Winner: Arya. Until his demise, the Night King was cleverer than the forces arrayed against him, and being able to resurrect people just by raising your arms while smirking is pretty devastating.
Who's had the better character development?
Arya started out as a dewy-eyed kid who liked to play with swords, while Tony began as a self-centered billionaire playboy who built weapons for the military. By the end, Arya was a trained assassin hell-bent on revenge, and Tony builds (and rebuilds) a team, and sacrifices himself to save everyone.
Winner: Tony. While Arya's character development is significant, it's focused on her getting even for the wrongs inflicted upon her family. Tony's motives are ultimately more altruistic.
Tony Stark. He just edges out Arya, owing to the greater number of people he's saved, the greater character development, and the fact that he can take a beating —and ultimately sacrificing himself in the process. But we'd be just as glad to have Arya on our side. And she has yet to face off against Cersei.