I have been on a case-buying binge recently in that elusive attempt to find the perfect case and failing dismally. I always seem to go back to the Midnight Blue Apple Leather case I bought the same day I got the phone. Anyway, I currently have the Ringke Slim in Clear and Gunmetal (with logo cutout), the Ringke Fusion Clear and the PowerSupport Air Jacket in Black (rubberized). I also tried the PS in Clear Matte but the "matte" finish was already peeling off when I opened the package. Exchanged it for a Clear Air Jacket which scratched the first day and was too slippery. Exchanged again for the black. My thoughts with my Space Gray 6+:
Ringke Slim Clear: Fits well but a bit slippery. Hasn't scratched yet. But overall, I just don't care for the looks of this case on the phone. Even though it's clear it doesn't really "blend in" with the phone and almost looks a bit tacky. Also it has rough mold marks along the sides.
Ringke Slim Gunmetal: Actually a pretty awesome case. Kinda wish I would have gotten the non-cutout version but they do include protective film to cover the logo. Don't think that's really necessary though. Nice snug fit and the color blends in with the phone. Not as slippery as the clear and smoother mold lines on the sides.
Ringke Fusion: Almost my favorite of the Ringke cases. I like that it offers more protection with the TPU bumper and it looks better on the phone than the clear Slim. Perfect fit and grippy too. My only gripe is what most others praise: the dust caps. The lightning port cover gets in the way when docking. I might just snip them off.
PS Air Jacket Black: Nice smooth edges, somewhat grippy but not a perfect fit. Mine creaks and wiggles a little. Black color looks good on the phone. I am not very confident the finish will last very long though considering my experience with the clear matte version.
I also picked up the "black" Apple silicone case and I find myself mostly leaning towards this one and the Apple leather. They both fit great, feel great, look great and give it just enough grip and a little extra protection without the bulk. The open bottom doesn't bother me very much since it makes it much easier to dock. I'm a little concerned with reviews on the silicone saying it peels after a month or so.