I have the Nokia Lumia 930 (pretty much the same as the icon) and I love it.
The reasons I choose the Lumia over the htc would be; camera on the htc is pretty bad to say the least, and you get the AMOLED screen on the Lumia with deeper blacks, higher contrast, and an all round better experience
Reasons I would go for the htc;
Some will argue a nicer design, and the htc has an included micro SD card slot. You also get a better audio experience with BOOMSOUND speakers.
Personally I would go for the Nokia Lumia icon because I prefer the design and the camera aspect of a phone is pretty important to me. That's just my opinion though