I use and love the Invisible Shield. I am currently testing another brand on 3 of our homes phones, but I have new Invisible Shields bought and paid for, just waiting for me to decide the free ones from StealthGuards.com are not going top cut it.
So far, I am pretty impressed by the Stealth Guards though, I have it on 2 HTC Imagio phones adn a Droid2, I got the full body kits. Fit nice, so far (4 days) the adhesive appears to be great and the clearity and touch is just fine. The Invisible shield had a bit more of a rubber-like feel to it, the phone would sort of cling or stick to an otherwise smooth surface or even to the dash of your car. This has a bit less of that feel.
Scratch resistance is something I'm going to determine from normal use, I'm not looking to gouge them with car keys and "try" to get them to scratch. I am sure I'll drop test them in my normal day to day use, my Imagio seems to think it is a basketball.
I like the Invisible Shield very much and to me it is the standard I compare others against. With a couple years of use with the brand it has not let a scratch get to the phone yet. I'm pretty tough on my phone, I take them camping, kayaking, riding my dirt bike... everywhere. I'm no office worker...I get banged up and bloody and my phone is right there with me!