With White Walkers practically knocking on King's Landing's door, the fight for control over Westeros almost seems like a nonissue. But if the latest Game of Thrones teaser illustrates anything, it's that the battle in the North is only part of the story's final chapter. The matter of who will sit on the Iron Throne remains in play, and although the show has gone to great lengths to set either Daenerys or Jon Snow up as the future leader of Westeros, those two lovers appear to be doomed. Having either (or both) of the Targaryen heirs end up running the Seven Kingdoms feels far too obvious for a show that loves its twists — not to mention the writers' gift for playing the long game. This is partially why we believe Tyrion Lannister is going to be the person who wins the figurative game of thrones.
As Quora user Murali Vallimanalan points out in their breakdown of why Tyrion could win the Iron Throne, there is a fan theory that suggests the youngest Lannister is actually the Mad King's son (and Daenerys's brother). However, Tyrion doesn't need to be a secret Targaryen in order to take the throne. The show's been laying the groundwork for him to become king since the story began. Look back at everything he's accomplished so far: King's Landing was at its most peaceful after Robert's fall in season two when Tyrion is in charge, he's the man who lead the charge in the Battle of Blackwater, and he cultivated a sense of trust among his allies like Podrick and Bronn. Tyrion consistently puts the realm first, not out of a desire for power — as his sister does — but because he knows what it means to be overlooked and deemed unimportant, just as the small folk often feel when their basic needs are disregarded during times of war.
Tyrion also possesses the necessary skills to lead. He's fair-minded, a tactical thinker, and a gifted politician. By comparison, Daenerys leads with force, demanding the Tarlys bend the knee or die. She's excellent at liberating people, but she's shown no aptitude at making the necessary political decisions to help them transition into free lives in a peaceful society. Sadly, she tends to leave chaos in her wake in pursuit of her rightful place on the throne. Meanwhile, Jon is an excellent warrior, but he's not a wise king. Wise kings don't bend the knee without consulting their people. Like Daenerys, he fails to listen to council or think before he acts.
Since this is Game of Thrones that we're talking about, the best candidate isn't guaranteed to be the one who ultimately wins the game, but there are hints that Tyrion is maneuvering the necessary pieces into place to take the throne. Remember that worried look he gives the camera as he watches Jon enter Daenerys's room in the season seven finale? I doubt that look has anything to do with jealousy, and everything to do with a dawning realisation that neither Daenerys nor Jon is going to listen to his advice if they have one another. That's bad news for Westeros, and Tyrion knows it.
Tyrion is the ultimate chess player, and he's maneuvered his way across the board into a position of true power. He is still the Hand of the Queen, and with another theory going around that he may have directed Cersei to lie about sending her troops North in order to keep Jon and Daenerys's focus on winning the war against the Night King, Tyrion may be working on stageing a coup. He'll wait until the Night King is defeated, of course, but given everything he knows about how the Mother of Dragons leads, he may very well betray her before the show ends. (That's if he hasn't done it already.) That sets up an endgame where Tyrion and Cersei face off, rather than Daenerys and Cersei, and that's a battle that would be grounded in a much richer sense of character and history.
If Jon and Daenerys fall in battle, the remaining players on the board will likely back Tyrion as king. Sansa will remember his kindness, Jaime is wise enough to know his brother is a better candidate to lead than their sister, and while in the North he will no doubt continue to cultivate strong bonds with the small folk. By the time the war with the dead ends, Tyrion is going to look like the only viable candidate to lead — even if he's not a Targaryen. The best part is, if he does become king, it will prove that Westeros is finally ready for progress — a leader will not be determined by blood or brute strength, but rather through wisdom. And as the character who most embodies the truth that cleverness and smarts matters more than blood or skill with a sword, Tyrion's win would be the most fitting end for the series, and the best possible outcome for the Seven Kingdoms.