If I use a case I'll use my bumper. Mainly because I have a silver metal back piece on my phone that I replaced the back glass with. So I like to show that off, and I like how the bumper adds a little grip to my phone.
Want to go "naked" but too scared to do so. Ordered the ION4 from ElementCase and love it. Not bulky at all and gives all kinds of protection. Paid $40 for it but well worth it. And it looks really good too.