It's been my experience that greased foil liners work best in this recipe. There's more of a sticking issue when using paper liners, even greased ones. I know that some worry about aluminum foil touching their food, so if you prefer paper liners, it should be okay. They might stick slightly to the liners, but it's not too bad. But foil liners do work better. Another option might be silicone baking cups, if you're not opposed to those, although I haven't tried this option myself.