Cases are a very individual thing, and dependant on what level of protection you are trying to achieve. Here's mine (below). It's not the ultimate in protection, but it
does extend out front and rear, so will protect the phone from short drops. The metal bumper give it a whole 'nother look though, and because the buttons are CNC overlayed, not just cutouts exposing the device buttons, it is completely sealed from dust getting in there. The back is a replacement (real) carbon fiber back cover, not a cover. Here are the eBay links where I got mine. If you want the for the bumper and end up buying it somewhere else, be sure you get ones with button overlays. Otherwise the device buttons will be recessed and hard to reach.
Carbon Fiber Battery Door Back Cover Case for Samsung Galaxy S4 SIV I9500 | eBay
For Samsung Galaxy S4 s IV Real Aluminum Metal Bumper Frame CAS3 Screen Guard | eBay