i've used sheets . no problem with whites, but the dark ones lose their new look after washing. that crisp color is gone. as for thread count, bring it on. i don't mind changing a needle in exchange for a backing that lasts forever.
i've even wrapped the edges and they do not wear out at all. i've been very satisfied. i only use cotton and i pre-wash, especially darks. i buy or make matching pillowcases. one twin sheet will give you four pillowcases, if you don't mind ones with seams all the way around.