I just looked at an unboxing of the Vaja case on YouTube and it's an absolutely beautiful looking case. My only problem with it is that it leaves the top exposed in the case of dropping the iPhone. If it had covered the iPhone better I'd be ordering one now.
I have a Case-Mate Naked Case that is very similar to the Rocketfish one. I like that it covers the front but the case screen sticks to the iPhone screen a lot. I just give a the case a little squeeze to separate it from the iPhone. The "click-snap" back clasp scratched up the back of my iPhone . Dust also sneaks in there and every once in awhile (like every 2-3 days) I have to take the case off and wipe off the dust inside. There's a clip holster that you can get separately but the clip is pretty weak IMO. (There's a case/holster combo too.)
i disagree with the front of the iPhone being the most vulnerable part. quite the contrary, in fact. After 17 months, the glass screen is the least damaged part of my iPhone. And this is a v1, which has an aluminum case. So on a 3g, i would definitely say the plastic case is most vulnerable to damage.