I have used a Power Support Anti-Glare screen protector on it since the iPhone 4. Minimal impact on clarity, protects the screen but the main reason I use it is the feel. LOVE how it feels on my fingers. They just announced that they are selling for the iPhone 6 this morning (they are also the company that has the anti-glare protectors in the Apple Store). Good luck.
Whatever you do, don't get the Zagg glass for it. I got it on my 6 and it looks terrible - it does not cover anywhere near the entire front of the phone, and the box said nothing about case friendly.