I've been an iPhone user for the past five years, except for a few weeks in 2011 when I used an Android phone to see how good it was. At that time, my evaluation was that Android was a second-rate knock-off of iOS.
But, with the releases of Android 4.0 "Ice Cream Sandwich" and 4.1 "Jelly Bean", Android got a lot less ugly, and hardware is finally fast enough that it doesn't feel so slow. Because I make about half my income from Android app development, I decided it was time to give Android another try as my personal phone. I vowed to put the iPhone away, buy a top-of-the-line Android phone, and use it for at least 12 months. My goal was to immerse myself in the Android ecosystem and learn how "regular people" use their Android phones.
When I made this purchase in July, the two top-tier Android phones were the Samsung Galaxy S4 and the HTC One. I've hated the two Samsung devices I've owned (Samsung Galaxy S and a Samsung Galaxy Tab 2 7.0), so it was an easy choice.
I won't re-hash the things that all the other HTC One reviews say. These are my personal impressions, and what I do and don't like about the HTC One may not match your preferences.