We propose a simple yet rich model to extend the notions of Nash equilibria and correlated equilibria of strategic games to the quantum setting, in which we then study the relations between classical and quantum equilibria. Unlike almost all previous work that focused on qualitative questions on specific games, usually of small sizes, we address the following fundamental and quantitative question for general games: How much "advantage" can playing quantum strategies provide, if any? Two measures of the advantage are studied, summarized as follows.