In the end, it depends on what you want and what level of protection you think you need. A case will give better protection than a skin if you're into extreme sports, for example. But any of the skins gives fine protection for everyday use. I use a Cocoon for mountain biking, and either a Lajo skin or Apple's belt clip for general use. I'm happy with all three, but the Cocoon gives full protection (ie, you can't get to the iPod) so you'll need the iPod remote too.
I have bought two cases. Both iSkin. One for my mini and one for my 60gb photo. They are really good. You have full access to the wheel and a screen protector. Only issue is you can't easily stick it in a docking station, you have to peal the skin back (refrain for childish joke). It does have a flap to insert the charger cable and usb thingy. You can also access the bit on the top (headphones & lock).