Not trying to dissuade you or anything, but I have an HTC One which I traded to my friend for a Galaxy S4. I regret it horribly. Everything from fit to finish, HTC One is the better phone. Camera-wise, it's a toss-up. Everything I used on my HTC One, I feel it took "generally" better photos, while, once in a while, the photos on my Galaxy S4 was much better than HTC One, but generally they were inferior to what HTC One took. Unless you are taking photos with your phone to blow it up on poster size, it's not much of an issue either way.
UI-wise, Sense 5 is infinitely better than TouchWiz, from design and thought. S4 UI design feels convoluted and and lack of a general direction in what they were trying to do, therefore lacking consistency.
Removable battery and expandable memory is nice, but going from 64GB (Developer Edition) -> 16GB (S4) internal memory space makes me worried about the apps that I install since it feels a lot "tighter". Sure you can use root and mount folders to SD Cards, but that's more of an annoyance. As for actual battery life, from my experience of daily usage on both, I feel that while HTC One has a smaller battery, it seems to last longer than Galaxy S4.
It is definitely true that the HTC One is incredibly hard to repair, however if you get a faulty unit, why wouldn't you ask HTC to repair it or exchange it? If you're really worried, getting any warranty (Squaretrade, Carrier or otherwise) would alleviate that problem.
Another point, which is just for me, AT&T and Verizon Galaxy S4 has a locked bootloader that is annoying, while its hacked, AT&T pushed a MF3 firmware update which disables the crack of the bootloader. Being at the mercy of the carrier because they handed a bag of cash to Samsung is quite annoying to me. IF you were to get a Galaxy S4, perhaps the GPe model would be better, that way at least you can flash whatever ROM you wanted.
HTC One on the other hand, while it is locked bootloader, you can pretty much have it unlocked through HTC website at your at your leisure. So you can switch ROMs all you want, heck you can even get Developer Edition and switch it to the GPe ROM and get updates directly from Google while having 64GB of space (much more cost effective, since GPe with tax costs about the same as Developer Edition).
Sorry about the wall of text
