Defender is the way to go
I had one on my 3GS and have had one on my 4 for about 2 weeks. If your concern is protection, not glamor, it's the way to go. As far as attracting dirt and fingerprints, I keep it in my pocket or laying around the car and have had no problem with lint. And really no problem with fingerprints. I get some french fry oil on the screen now and then, but it readily wipes off with a damp cloth. The only thing that takes getting use to is buttoning up the little flap on the bottom that covers the dock connector. You have to line it up just right before it fastens tightly.
As far as the reviewers who complain about loose fits, I haven't experienced that but then I don't take it off and put it back on. Perhaps it stretches if you do a lot of that.