I have a few different brands of square pans, but my absolute favorite have been “Magic Line” brand. I think they have the sharpest corners and straightest sides, but that’s just my opinion. I bought mine when there was a small sale on them at GlobalSugarArt.com. They aren’t super expensive and I just think they’re fantastic!
Good luck! :)
Baker from The Epicurean Delight - Falls, PA