I have used the HTC One for 1 week before going back to ATT store and exchange for a GS4.
Reasons being:
1.I couldn't get enough details on the pictures I take with the One. Most of the photos I take are between 10am and noon somewhere outside, and that's where GS4's 13MP shines. HTC One's 4MP photos also look blurry on my 1440p screen(3.5MP).
2.The larger Screen(13% larger), I prefer AMOLED's more vibrant color as well. The darker black also looks better since I watch videos a lot in dark room or conditions(in a plane). HTC One's smaller screen looks even smaller when surrounded by the wide bezel around it.
3.HTC One's battery life is worse than GS4 from my experience(based on my usage model), most of my screen time are spent watching videos or reading ebooks(Google Play books have black background white text option) which is advantageous to an AMOLED display phone's battery life.
4. For $290 I can get a 16GB GS4, 64GB Samsung Micro SD card(10 year warranty, total of 68G Useable space) & A good case for my S4, while for $300 I can only get a HTC One 64GB(Total of about 55G useable space). Since I need the media storage space for my 50G of video I watch+ Photos/Podcasts/eBooks(need those on the plane so cloud is no go). This is pretty much a no brainer.
5.I prefer GS4's Size(shorter/wider) and button layout(power button on the side instead of top).
Things I still miss from HTC One:
The dual front facing speaker(Samsung need to figure out a way to have this for their next phone, I suggest remove the physical home button and put a speaker there, then enable to ear speaker up top to work for media playback).
Truth be told both are great phones, it just happens GS4 is the better fit for my usage model thus the better phone for me.