I owned the HTC One before the S4 before I sold it. Had both of them to play with, and decided to keep the S4. Here's how I break it down:
Samsung s4
Pro's
* Micro SD card lets me get 80 GB Of storage, while it isn't the same as internal storage most large games or applications can be sent to the SD card in entirity. Bard's tale, Modern combat 4 (I think it's combat), Need for speed if I remember correctly also went to my SD card.
I agree with pretty much everything asanatheist stated, so I'll give my feedback on his points. This is one of my favorite things about the S4. I had the One before, and even though it was 32gb, I still missed having the SD support. I've got the 32gb AT&T version of the S4 and a 64gb SD card...96gb. That's just insane. I'll never need all of it, but it's nice to have the option.
* Removable battery: Single battery is far less space consuming than the S4's charge/cable. Takes 3 minutes to swap and you can easily slide the battery into back pocket and forget about it.
The ability to swap batteries is always a game-changer for me. While I'm usually near an outlet, there are times when I'm not and it's nice to know I can just swap out batteries and not have to worry about juice.
* The Screen on the S4 is definitely better overall. I consider my self a screenphile. Love my high quality IPS panels. However the S4 does have some major advantages. Contrast, response time, and appeared brightness (Doesn't require diffusing films). Lastly since the Amoled's dont require backlighting, they appear brighter than LCD's which have significant light dispersal from the diffusing films.
Many people including my self do not like the unnatural colors of the S4 but we're forgetting that the S4 is a wide gamut panel. It isn't that it's saturated but the fact that applications are not managing the color reproduction properly. Professional monitors require wide gamut to accurately represent ALL colors not just some and suffer from this saturation just as easily as the Amoled panel in Samsung smartphones.
I'll differ a bit here, but I do think the screen on the One is a touch better than the S4. But that's purely from a brightness and white balance standpoint. I'm not a big AMOLED vs. LCD person...as long as it's good, I'm good. But the screen on the S4 is amazing (especially compared to the S3, which looking back, was awful in comparison).
* Way better camera. The HTC One may take okay shots but when you compare them side by side it's impossible to pick the HTC One's camera over the S4.
One of the things that made me sell my One and move to the S4. I use the camera constantly, both in my personal life and my job, and I need a camera on my phone that can take great pictures. The One's camera, while OK for social networking posts, is DREADFUL when it comes to anything else. It's one of the things I absolutely hated on the One. I loved pretty much everything else, but the camera was a deal-breaker.
* Battery life is way better on the Samsung S4. On the HTC One I constantly had to carry my charger and charge the device by about 3pm. On the S4 even with heavy use I made it out of work with about 20% left. During lighter to medium usage, I leave work with about 40% to 50%.
I agree with this 100%, plus I'll add, the S4 charges SOOOOO much faster than the One. Another thing that annoyed me about the One...it takes FOREVER to charge.
* Lastly while the One should be more comfortable in the hand, the light weight feel of the S4 really makes the comfort level on the S4 and HTC one kind of even.
I loved the way the One felt in the hand, but this is spot on. The light weight of the S4 makes a world of difference (even with a UAG case on it). I love how light the S4 is.
HTC One Pro:
* Aluminum chassis looks great, and feels premium but to me having spent 2 years testing and researching what I could about laptop constructions understand that Plastic>Aluminum when it comes to exterior shells. It's better in terms of protection first and foremost, and secondly cost and servicing.
I like that the S4 isn't unibody. While it looks great and feels great in the hand, it's a pain to service. Another spot on point.
* The speakers are the best in smartphones right now. People need to stop saying their loud. They are NOT loud, chances are you will NOT hear while showering or somewhere loud. They are just far more defined, clear, and have more dynamic range and bass than other phones, less artifacts and sound issues.
This makes it seem louder because you hear far more details at lower volumes but they are NOT louder. They are just perceived louder. As I tell anyone who doesn't understand why I have $180, $250+ headphones.. You need good quality speakers capable of reproducing most if not all ranges of frequencies used in music regardless of volume (current) going through the headphones.
Yes, yes, YES! Finally someone says what I thought during the entire course of owning the One! Yes, the speakers sound great...but they're not loud AT ALL. In fact, I couldn't believe how quiet they are. It's really something that was a huge letdown for me.
* HTC Android Sense UI is quite a bit more stable and lags less (not much difference but it's definitely more stable as there are less crashes) than the S4's, although it is outdated (4.1.2 versus 4.2.2 on the S4 versus 4.3 currently on Nexus devices). The experience I had with the HTC one for the month was nothing short of excellent. Very iOS like in terms of stability and responsiveness, again the S4 is no slouch and keeps up fine 98% of the time once you update firmware. I can't really find a good analogy because the lag on the S4 is not as significant as some make it out to be, at least for my S4 (Stock firmware, stock 4.2.2 stock everything).
I agree with this as well. The lag is there...but it's not awful like some people would have you believe. Sense 5 was smooth, but I did experience some lag as well, especially when scrolling through home screens.
* Better Internet browser on the HTC one.
This isn't a big deal to me as I typically use 2-3 different browsers. But I do think the One's stock browser is a bit ahead of the one on the S4.
That's about all I could come up with for now.