Best for what use? If you use it to prop open a door, you want one with the heaviest box. If you need to carry it around from place to place, you'd want a light box. For eating, you'd want one made with natural materials.
If you want free, you want Linux, several popular ones out there, Ubuntu is a good one.
Mac Os is my favorite for everyday computer usage and I would say its the best. Windows is the only choice for running PC games, so its best for gaming, from a certain point of view. And Linux is free so for a HTPC, its best also from a certain point of view.