Hoodman hard plastic.
You don't really need one as the screen is supposedly nigh on unbreakable anyway but I'd rather spend £20 on a protector than probably several hundred on a new screen if the worst does happen.
The Hoodman one is far superior to those crap GGS stick on ones which will just shatter and leave your screen covered in loads of tiny shards of glass, I've seen it happen, it has a small gap between the screen and it so if you do smack it off something it can give a little without even touching the screen itself.