My incipio DualPro Shine works on both 6 and 6s. Honestly it is one of the best phone cases I've ever used. I'd highly recommend it.
Link here.
I've always hated that whole line...and I've had to use those cases temporarily on my iPhone 3G, 4, and 5. I've also used them on a Galaxy Note 2 and a Galaxy Note 3. Now, I'm really drawn to TPU-material cases that offer just the right amount of impact protection while staying slim and pocketable.
Incipio's "NGP" material is really a kind of TPU. The Incipio NGP cases are great. I've used the black "Incipio NGP" for iPad mini, iPad mini 2, iPhone 6 Plus, and iPhone 5c.
For the iPad mini, mini 2, and iPhone 6, I used a razor blade to cut a small slit beside the volume and lock buttons and tactile feedback is greatly enhanced. That wasn't necessary for my mother's 5c.
Incipio Frequency is also made of "NGP" (TPU) material. I tried the Incipio Frequency with iPhone 5, but I didn't like the way the lock button felt in the store (of course, I didn't try the enhancement). The Incipio Frequency for iPad touch 5th gen was absolutely perfect and required no modification. Amazing tactile feedback.
The Belkin Grip Candy Sheer for iPhone 5 / 5s was another great TPU material case that looked great and protected my phones very, very well.
I'm still using an Incipio NGP on my iPhone 6s Plus and it feels absolutely excellent. I feel like I'll never need any more impact protection than what I have, and it's super slim.