Polyester! It's the most optimal of all materials you come across for various reasons. For starters, it doesn't wrinkle or allow moisture-build up. You don't have to worry about ironing the pillowcase every time to make it look presentable or worry about sweating all over it. However, polyester isn't very breathable, which makes it unsuitable for hot weather. But regarding durability and outlook - there's no material better than polyester.