Pickiest when it comes to pnm?

Which sorority is the pickiest when it comes to choosing pnms? I know there are rankings and based on that it’ll be harder to get asked back to top houses but I feel like certain houses are pickier like AOII and ZTA compared to ChiO which is like on a similar tier. I wonder why and I esp feel like you can see how picky they are based on their 2nd round selections