Technically, any game that has gameplay-affecting components that can be bought (and not only earned through in-game play) is some degree of pay-to-win. I would say that Dota 2 and CS:GO are not pay to win, as they do not sell gameplay-affecting items.
Thus, TF2 is pay-to-win. However, it's very low on that scale because you can easily get the weapons through drops and trading and crafting.