I have the black leather case on my 6 since launch last year. It's starting to show some wear around the corners, but it has served its purpose admirably by protecting my phone from several drops onto a variety of surfaces including tile and concrete...
Phone is still mint for all intents and purposes, and the case looks pretty good to me eye... But ymmv...
Pros: thin, light,classy looking, raised edge helps protect screen during corner drops.
Cons: expensive, no screen protection for direct screen contact, leather ages quickly (may be a pro if u like that look)