My understanding is, due to how Windows Phone OS is setup, high end models of the phone run only on the S4 chip by Qualcomm as of now. So all the four new Windows dual-core phones use the same internals. What differs is the screen, the camera and probably some hardware features such as noise cancelling microphones. Right now, Nokia has the bigger screen in about the same size as the HTC phone. 4.5 inches to 4.3 inch screen. It will definitely have the better camera without a doubt. Also, it has Nokia Maps which is pretty cool. Mostly HTC will have the same as a rebranded Bing Maps, but that's not sure.
Look wise I'll prefer the matt finish of the HTC to the glossy one of Nokia. Both are polycarbonate unibody, so durability is about the same I guess. The only thing remaining is the price. Also the HTC one will be available in November, no dates have been mentioned about the Nokia yet.