Slider case
Got the white slider for my black 3G. It protects well, for sure. It can be mightily difficult to take off, and can cause a light scratch on the back of the phone along the grip strips of the case.
Flick case
This is the one I'm using now. It's much thinner in your hand than the slider case, which feels great. It also allows you to see a bit of the chrome around the phone, which I love. Due to each of these things, however, it isn't quite as heavy-duty or protective around the chrome as the slider, but I still prefer it.