I'm not a big thong fan.
Mostly when I buy them, it's because I thought the design on the front was really cute, or they match a bra I have. I don't wear them very often.
They've gotta be pretty loose to be comfy... and cotton.
My butt isn't the best though, and it looks MUCH cuter in boyshorts (don't know if that's the proper term, the ones that are like ultra short hotpants) or a bikini cut. Those are my panties of choice.
Oh, and really, I don't think they look great on girls, even ones with amazing asses.