Swerve vs Danielson is my current choice, but I think the Women's Belt is due to main event a PPV eventually and this is the strongest case it has to main event since AEW started.
Of the current AEW titles, the only ones which have not main evented a PPV are the Continental Championship (which is relatively new and primarily acts as a Tournament crown defended occasionally throughout the year and then the Classic at the end of the year) the Trios Championships, and both Women's belts. I think in part it has not happened yet for the women is because the AEW Women's division had the least star power at first, and it has taken a long time for the Homegrown stars to get over and to draw enough big star talent. That and the booking of the division was not as consistent.
Now though, the women's division has been one of the best parts of AEW this year with Mone coming into her own once winning the title and fully embracing being a villain. Willow has become a star. Kris has been great. Julia was a good TBS Champion minus her injuries. Thunder Rosa silenced some haters with her recent work. Shida's still amazing and even if she isn't always on AEW TV since she travels back and forth a lot between Japan, the fans have grown to love and appreciate her. Hell, even Saraya and Harley have become an endearing mid-card heel act with Saraya capable of being in either title picture and Harley, even if she's still learning the ropes, is fucking hilarious. The spice on top has been this storyline.
Mariah is a fucking star and Toni has THRIVED with her Timeless character to the point where I think she's gotten comfortable enough where if she eventually sheds the Timeless character, she can do a lot better than before as herself in terms of showcasing her mic skills. Since she's always had the look, been amazing in the ring, and at least some star presence, just didn't have the talking ability to take it to the next level. She has now.
On the other hand though, even with all that, in terms of star power, Danielson has both beat especially if this is his potential last World championship match of his career and Swerve has gotten over and thrived as this anti-hero. Historically, that match has major significance beyond a first time thing. Because it may be the last. There will be chances for the first women's main event of a PPV/PLE in AEW history again. May not have another chance for a Danielson world title match/win.
The match too has a great level of unpredictability. Danielson has said in interviews OOC he didn't have the goal of winning titles in AEW. But of course, he's a natural troll. If there is a time to give him a short title run to give him his flowers, then this would be a great time. He wins it, defends it in Chicago, then maybe once on TV before having his "full-time finale" at Wrestle Dream. Even without the title, Swerve has the storyline with Hangman he can jump into which is personal with or without the title. On the other hand, Swerve has been legitimized when he beat Will. If he'd drop it at All In, his reign would still be good, but there is still legs in it, especially with the return of Hangman who may be the perfect person to beat him for the belt. (Hangman did nothing wrong). Danielson can still, after losing against Swerve, have a mini-tour in TV where he hand picks opponents for him to face. A mix of never before seen matches and scores to settle before his final match as a full-time wrestler.
So long story short, either or would be great and worthy main events, but my gut goes with Swerve/Danielson.