WITHOUT a case looks the best, imo.
in fact i would roll without one but as soon as i do that i'll drop it,
then everyday when i see the marks/scratches i would kick myself for not using it.
I love the look of the iPhone naked. If it couldn't scratch or break I would never put a skin on it. But it does, therefore I do. A slider case actually scratched my first iPhone. I was able to get a replacement and was smart the second time around and got a soft skin. Now it is protected and still looks good.
I like it better without the case as well however mines been cases since day one. Keeps it "new" looking since my little one plays games on it when she gets bored in the car or store.
I thought naked was good too but I've found that it easily falls out of my hands so even a thin case provides more grip and doesn't look all too bad. Any of you guys use the Seidio Innercase 2? I'm really interested in getting that as it actually adds style (difficult to fathom I know) to an already stylish case.
Definitely a matter of opinion, but I think Apple's design guys do far better than most case manufacturers. That said, it's sad to see a broken screen or major scratches because it was left caseless.