When you get down to it, Cersei is on of the more sympathetic leaders. Since no one is suggesting Davos or Gendry for the Iron Throne, there really aren't any good choices. I mean, there's several characters from the books, but they really aren't here, so based on what we've got to work with, it's Cersei by a nose.

Cersei on the show, yeah. Twincest, yuck. But in this setting, it's a little more acceptable than normal, and the narrative over the last few seasons more or less equates it with all other not traditionally accepted sexual relationships, like homosexuality and so forth. And there's the treason thing, but Cersei on the show made an effort to bear Robert's children, had a baby by him and lost it. Having Lady killed was spiteful, but no one seemed to care that her son had been attacked and injured by the pet monster of a girl who also attacked him on speculation that he might kill some peasant. On the one hand, she had Robert assassinated, sort of, but on the other, he was abusing her and raping her, and was about to be given information that would motivate him to murder her and her whole family. Her brother had to flee for protesting the arrest and imprisonment of their totally innocent & disabled youngest brother, so it's not like there was anyone she could turn to for protection.

And once she managed to secure the throne for her family and neutralize their immediate foe, she had to, with one hand, prepare to fight Stannis and/or Renly with much less help than she had in the books, and a brother she had reason to believe meant her harm, and on the other, rein in her psychopath of a son, who grew up with Robert's example of self-restraint. We see Cersei on the show explaining to Joffrey the limits of royal power and the need to act through the feudal structure, but what can she do when he doesn't listen and has all his bastard (supposed) half-siblings massacred and has a Kingsguard try to murder the guy responsible for defending the city, in the middle of a battle?

Then she has to endure several years of condescension & bullshit, with people telling her that as a woman she has no business on the Small Council, while Olenna Tyrell is sitting RIGHT THERE, the Tyrells who secretly murdered her son and framed her brother, grabbing for power by molesting her surviving son (any kid as ignorant of sex as Tommen acts when Margaery seduces him is in no position to make an adult choice) and using sexual enticements to alienate him from her. Cersei is publicly humiliated by the Sparrows, while Margaery gets to hang around with all her clothes and hair. No one takes the Dornish threat to Myrcella seriously and Tommen kills himself because of his psychological dependence on his molester.

I honestly don't blame her one bit for dressing in black with villainous shoulder pads, much less blowing up the religion and noble family that did most of this crap to her.

And she, unlike just about anyone else, is at least doing something right. She's keeping the crown's creditors happy, the people of the city are no longer rioting, there are no fundamentalist cults trying to run a grassroots theocratic dictatorship in the capital city, and judging by the cheers of Euron leading his captives through town, her regime is pretty popular. Yeah, there's the treachery, but on the other hand, she said she'd trust the verbal guarantee of Ned Stark's son that the Stark-Targaryen alliance wouldn't turn on her after the fight with the White Walkers, and HE WOULD NOT GIVE IT! He basically told her to her face, "If Dany wants to kill you, I'm going to help."

In contrast, Daenerys is an entitled little twit who bullies people because she can, murders people on the spot for NOT betraying their sworn oaths and in a truly Egwene-like strategy, decides to starve out a capital city, rather than directly assault the leaders in their separate and distinctive building, because of bad optics. Her own followers think she's a psychopath who needs a patricidal alcoholic dwarf to keep her under control.

Speaking of whom, Tyrion is a condescending little shit who doesn't have Book Tyrion's trauma to excuse his premeditated murder of his father, since his first "wife" actually WAS a prostitute. He was a complete failure as regent in Meereen, first arrogantly dismissing Missendei & Grey Worm's views, when they had been following Dany since she began her anti-slavery crusade, and actually KNEW something about the region, its politics and the character of the slavers. Then he made a deal with the slavers, which they broke and began besieging Meereen, which was only ameliorated by the surprise arrival of the Dothraki & dragons with Daenerys. And for this she makes him Hand. Since then, he got out-thought by both of his theoretically stupider siblings, with Jaime's military strategy and Cersei's negotiations, and has utterly failed at Varys' appointed task of keeping Daenerys' pyromaniac tendencies under wraps. To whatever extent she's been behaving since the latter half of season 7, it's pretty much been hormonal-driven, due to her sudden crush on Jon.

Jon is supposedly the rightful heir to the Iron Throne, but he's a complete moron when it comes to military stuff, at least since his resurrection, and diplomacy, for that matter. Against all advice, he goes to Daenerys personally, with no guarantees or safe conduct, gets himself effectively taken prisoner, and his subsequent success from then on has been entirely due to factors he could not have anticipated, largely Daenerys' whims. The ill-conceived zombie-knapping expedition was largely his idea, and seemed to be under his leadership, and reduced the good guys' dragon advantage from 3-0 to 2-1. And it turns out that bringing a zombie south served no purpose other than to recruit Lefty Lannister to the good side, and give Cersei more confidence going forward, seeing that they will be preoccupied by a legit threat and their northward preoccupation is genuine and not a feint, not to mention their draconic deficiency. And as far as ruling goes, his being out of touch with his kingdom caused a near-mutiny that was only quelled because of Sansa's loyalty. This being a girl who went through two weddings to her family's arch-enemies and got Stockholm Syndromed into being friendly with Tyrion (whereas the much less physically mature book Sansa refused to kneel at her wedding and never gave her husband-captor an inch, despite coming much closer to being maritally raped by him), so loyalty ain't exactly what you'd expect from her. Also, the brief stint of Jon ruling his kingdom showed he has no idea how to run a meeting.

Sansa is at least administratively and politically competent, but there was the aforementioned idiocy of going along with her marriages, and her performance prior to the Battle of the Bastards was pretty shitty, since she apparently withheld the new of Littlefinger and the Knights of the Vale out of pique that Jon & Davos & Tormund did not present her with an engraved invitation to share her thoughts in the war councils. Even though, when Jon DID ask her, she denied having any military knowledge to contribute and just kept yelling at him to not fall into Ramsey's traps or play Ramsey's games. When asked for specifics, she was not exactly forthcoming. Then she tortured a guy to death and smirked about it.

Bran is a lifeless freak who likes freaking out his oldest sister by bringing up things like her rape and their other sister's kill list, and can't even show any gratitude to the woman who lost her brother bringing him to and from the Three Eyed Crow's lair, and his understanding of politics is so bad that he believes Lyanna loving Rhaegar pretty much cancels out the legitimate grievances the rebels had against the Mad King, like his burning Ned's & Lyanna's father and brother alive. As Jaime testified to Ned way back in season 1. Good King Bran thinks Robert & company should have just rolled with all that, because Lyanna loved a guy who not only divorced his innocent wife to marry her, but disinherited their children together, and gave his son by Lyanna the same name as his living child! Rhaegar died before the Mountain reached the Red Keep! His death is probably why Tywin decided to attack the city in the first place. So if he named Lyanna's baby, it was a total dick move and if he was not involved, Lyanna decided to name her child according to ways of her husband's family, despite the atrocities her in-laws had perpetrated against that baby's uncle and grandfather!

There are no winners here. Cersei is the best of a bad bunch of choices.