I've had:

- OtterBox protector that came with the case. Smooth stylus action, and no scratches for two years. It's the thick, smooth kind that uses glue to stay on. After about two years it got a few bubbles underneath, and dust had gotten in at the edges (partly my fault as I had not applied it carefully enough; one corner was totally not adhering). At that point the protector had minor scratches from keys in the pocket. The screen was in perfect condition. No holes for the sensors.

-Phantomskinz - the thin, rubbery type. You dip it in soapy water to make it stick. Does not attract scratches, and offers a slight resistance to dragging a fingernail or a styles, which is not an issue with me. You get two for $10. Has holes for the sensors. Application is a bit of a hassle with soapy water, but there is a good instructional video on their web site and mine is sticking from edge to edge like an Alabama tick.