I've got the Toughskin for my 3GS and it's alright. It'll definitely protect the phone, but I hate the little plastic frame that goes around the screen.
However, I really like the redesign for the iP4. I like how the inner frame is now a clip-on case and doesn't mess with edges of the screen (and potentially screw up a screen protector). I also like the design of the outside of the rubber case.
I don't think I'd use it as an everyday case (for that I use an Otterbox Commuter), but if you're going into a rough situation, that Toughskin looks like it would do the trick nicely!