A variant of “free demo, paid game” is to have an episodic model, and have episode one free. I intend to do this with my next game, if I ever decide to realize the sequel.
This model makes the most sense to me, as long as your games maintain a shared narrative. If they don't, a free demo with limited capabilities is a similar approach. This way you don't lose players to the price tag, and people who have played your first episode/demo and like it are likely to pay for subsequent episodes/the full game.