Have the Yellow/Gray one for the 4S
I really like this case; I used the iPhone 4 version for a year, and it was great. I haven't noticed the screen protector being loose; there may be a very slight gap between the film and screen when the phone is in it, but it doesn't affect, as far as I can tell, the usability of the device.
The big advantage of the Defender is that when you insert it screen-in into the clip, the screen is completely protected short of being run over by a car. I don't like, with the 4S version, how the cut-out for the rear camera is so much larger. Much greater likelihood of something scratching up that area.
I used the Defender mainly on weekends; I had a Vaja case for during the week, now replaced with a Speck Candyshell Satin, which is awesome so far.