Another thing to remember, if you already have small scratches, some screen protectors (like Ghost Armor and I think Zagg as well) will "fill them in" to where you'll not notice them.
The great thing about Ghost Armor is that (around here) you can find them at a Kiosk in a mall and for $15 + $5 installation, they will put it on perfectly. It'll take a LOT of pulling to get them off, so no worries about slippage or peeling or coming up at the corners.
If there are issues withing the first 7 days, they will remove and re-apply for FREE. After that, you have a lifetime warranty where you can get them to remove and reinstall for the $5 installation fee only.
I have bought these for just about every touchscreen phone I have owned and not once have I ever had to have anything done after it was applied.