Purchased and used both. First things first, they are both great cases. Can't really go wrong with either. But for me, I prefer the Incipio more(I've only ever owned Otter box cases prior to the One). Just feels so much better in your hands. Nice rubber-ish feel. What I didn't like about the Otterbox was the very slick/slippery hard plastic on the back. That is the only real negative imho. Both are bulky, with the Incipio being ever so slightly smaller. The Incipio fit a bit more tight around the phone. I did like that the Otter box has covers for the ports(sans power button). That's a plus.
In the end, I returned the Otterbox because of the ever so slightly more bulk and how it felt in the hands. Both are great cases though.
Rob