DO NOT DO THIS!!! The wet-adhesive vinyl films SUCK on the screen. They're great for the back / casing, but for the screen stick with the static cling type. A good one will be indistinguishable from the naked screen. SGP Steinheil is my personal preference, but there are other good ones out there.
I have to agree with you here on the SGP one. I have one for my Samsung Galaxy S2 and it's as smooth as the original glass. It's made in Japan and has a very thing high quality feel that is super smooth and NO decrease in touch sensitivity. I've used Bestskinsever and they are OK but noticed that it decreased the touch sensitivity vs the naked screen on my iPod 4G.