The HTC One caught my attention solely due to its looks.It was just stunning to look at and my interest was piqued.
Thankfully the phone was good enough on other levels too that matter to me. Build quality is premium so you feel like you are holding an expensive gadget, display is mind blowing, best audio among all other phones.
The Sense 5 UI skin is a huge plus too..it just looks so elegant and is completely lag free. If you want to see exactly how lag free it is, try the following - open an app and come back to home screen, try switching between apps. Now go try the exact same thing on a Galaxy S4. The difference is very perceptible.
So glad this phone came around the time I was in the market for a new phone :)