I have the Spigen Tough Armor case and I absolutely love it. I'm definitely going to get the same case for my iPhone 6. I like it a thousand times better than the Otterbox Commuter that I used to have and I used to swear by that case.
I just went on eBay and ordered 2 TPU bumpers for $5.58 each. Should be delivered between 09/15 and 09/18 so my new iPhone 6 Plus will have protection from day one. I don't like bumpers with a back cover. As long as it has a lip on front and back, I'm good.
I am using the Slim Armor right now on my 5, but I may try something different on the 6. I was using an Urban Armor Gear case when I first purchased the 5 and I am considering this style again, but with the clear back.
At the time of my post it wasn't confirmed. A lot of case manufacturers were putting cases out there that won't precisely fit the new iPhones. I know - I have a 5.5" case that has the cutout for the power button on the top. The size is correct, though.