I'd say Little Finger. (Heavy spoiler alert! read at your own risk!): Petyr has no background, and no backing. He has nothing to fall back on and he fights alone. Tyrion has his family that he often uses as leverage; when he doesn't have his family to back him up, his life sucks. Varys has his mysterious foreign patron, from whom he obviously receives intel, networking, and finance support. Petyr has nothing. He has no family, no mysterious patron, he doesn't even have that much money (sure he owns some shady establishments, but compared to Casterly Rock and a Pentos billionaire ... it's nothing). Petyr sees through people, and he never lets his emotion gets in the way. All three of them have extremely good judgement on character. But Tyrion was betrayed by Shea, he has some serious father issue with Tywin. He manipulates people, but always have some reserve. Varys was wrong about Joffery (who end up killing Eddard, and messed up everything). The book doesn't really tell us how Varys manipulates people, he's taking more of a passive role. Petyr knows everyone's weak spot and sets them up to destroy each other. Petyr masterfully created the illusion of harmlessness. While people come and go, honored or killed, Petyr is always there. Everyone finds him useful, yet virtually no one feels threatened by him. While Varys generates fear and suspicion, Tyrion generates loathing and ridicule, Petyr generates nothing. Even Cercie (who hates almost everyone) find it hard not to rely on him. In this kind of power struggle, survival is the key and the best way to do it is to make yourself harmless. Petyr plays everyone. While other people simply react to what's happened to them, Petyr actively creates chaos, stirs up the dirt, purposefully sabotages relationships, creates suspicion, frames innocent people ... when everyone is fighting each other for reasons they don't even fully understand, he was laughing in his head. Yet, we're never quite sure about his exact goal. It seems he's doing this out of pure hatred and loathing for the aristocrats who despise and loathed him when he was little. That makes him extremely unpredictable and dangerous. In many ways, Petyr is the Joker in Westeros. He just wants to see the world burn. Tywin is a smart, cruel, great strategist, knows almost everything, can manipulate people like no other, can see the bigger picture, yet is still willing to get his hands dirty. He would make a great king if he could sit on the Iron Throne. However, we have to recognize his manipulation was largely based on fear and intimidation. He used his wealth and influence to buy/force people into doing things they might not like to do otherwise. That's less skillful compare to how Little Finger manipulates people. Because buying and threatening people will create resentment, you set yourself as the target. While Little Finger used persuasion and deception, he set up traps waiting for people to walk into them, he subtly nudged people towards the direction he designed. That needs a lot more planning, a lot more intelligence, and skill. On top of that, Tywin had one single fatal weakness: arrogance. Because he's so smart, everything goes as he planned, he dismisses any sign, any suggestion, any feedback that's different from what he had in mind. Most of the time, he's right (and that further confirmed his arrogance). But when he's wrong, the consequences are often disastrous. He misjudged his own son Tyrion, and he underestimated Little Finger. He was played, while he plays others. He's also a piece in Little Finger's game. (I should clarify, I actually like Tywin a lot. He's probably one of my favorite characters in the book. And I really don't like how he died, there're also some weird inconsistency in his character. But still, his arrogance blinded him to danger right next to him). I wonder what Petyr ends up doing with Sansa. If anyone can be "the" Queen, it's Sansa. (No, not Dany, I like the girl, but Petyr could play her like a violin.) This question originally appeared on Quora. More questions on Game of Thrones (TV series): Is the look of the Stark children significant? What makes Tyrion Lannister such a compelling character? Who is your favourite character in GOT? And, why?
