Impossible Project film, but it's pricier than I can afford these days. The Colorpack II has options, and I like having options. It works with Fujifilm, which has color and black and white varieties, and Impossible makes film for it, too, if ever I have some extra cash and want to give it a try.
I started out with a box of Fujifilm FP-100c color film. My first efforts were just sad, really. I'd never used peel-apart film before, and it just felt like the camera and I weren't speaking the same language. Today, out walking in the park with my dog and a friend, something finally clicked. The results are gorgeous and I am completely in love. And so the Polaroid obsession continues.