I don't know much about female underwear so I can't say much there. I know cotton and spandex are pretty stretchy. So maybe look out for those materials. And I've heard good reviews about MeUndies so maybe buy a pair from there.
As for male undies, I know Jockey is amazing for wedgies. Especially their briefs or athletic underwear. Old Navy's undies are also extremely stretchy. I can do atomics in XL Old Navy boxer briefs pretty easily. And I've bought XXXL briefs from really cheap brands like Hanes, Fruit of the Loom, ect. and I can easily do atomics in them. I've also heard good things about MeUndies and American Eagle but I haven't tried either of those. I haven't found a pair that's strong enough to not rip during a hanging wedgie. I usually use two pairs but I know many people only want to use only one.
BTW I'm 6'1" for anyone that wants to know my height. If I can do atomics and shoulder in these than most of you can as well lol.
If anyone knows any other good brands go ahead or materials then please tell us. We'd all appreciate it very much! Especially female underwear or underwear that doesn't rip easily. And also the reason I didn't name any expensive underwear is because the underwear I said already do the job at a much better price. Alright well that's all. Have a nice day!