I'm a big fan of case #1 and case #3. #2 is just a thin strip that looks like it adds protection. It would from scratches but nothing else. The leather one is leather, which inherently offers the best scratch/abrasion resistance (motorcyclist here), and #3 is hands down the best for adding actual armor/impact protection while also protecting against scratches. I'd go with #3 if I were looking for a spine-protector case.
Edit: for reference, I got this case which does not have spine protection. It's a thic-boy but man does the case feel solid. I had a nice spigen case on my 3 that was slim that fit the 4..well enough, but got an actual case meant for the 4. I think I like the thick one more than I anticipated. Thought I'd share. Best of luck in your decision!