[Galaxy S 5 General] crazeco:
I bought the Samsung GS5 and HTC One M8. I purchased both phones to use simultaneously for at least a week.

Camera image quality on good shots: GS5.

Outside M8:

Outside GS5:

Auto settings. I upscaled the M8 image to 16MP. I think IMGUR might automatically downscale. My overall impression is that the M8 takes in too much light. It’s difficult to avoid, even when playing with exposure settings. Once you zoom, the GS5 16MP really comes into play. You can be the judge on which images are better, and by how much.

Camera consistency:

M8. 50% my shots with the S5 end up a bit blurry. 75% of my M8 shots are in focus. That’s with still imagery.

Which is more important? Overall quality on excellent shots, or consistency?

The camera software on the M8 is better. There's an option to go 100% manual mode that lets you adjust color, exposure, ISO, shutter, and focus on the FLY. There's nothing like that on the S5, here's a pic:

Handfeel:

The S5 is easier to hold, especially when laying down in bed. The S5 is lighter and weighted in a way that feels like my hand is simply connected to the device. It doesn’t put strain on my wrist or make me feel concerned about dropping it at all. My confidence level holding the device without a case is extremely high. On the other hand, the S5 has a filmy/slimy feeling that makes it feel dirty. It always feels like the back of the S5 was rubbed on a slice of pizza. I feel confident holding it, but I don’t enjoy it. It’s very uninspiring.

The M8 feels amazing in the hand. I consistently want to pick it up for no other reason than to hold it. It has a nice cool temperature that is very welcoming. I don’t think the M8 is more slippery than the S5. I think it’s how the device is weighted. It’s harder to hold because it feels screen side heavy. When I’m holding it in bed, I always feel like the device is going to slip out of my hand and fall on my face. Not because the case is more slippery, but because of the weight. I am constantly reinforcing my grip on the phone out of fear of dropping it. It’s a strange mix of wanting to pick it up, and being afraid to pick it up.

I did use a GS4 and a Galaxy Nexus prior to these devices. I wonder how much of this is because I simply feel comfortable with a Samsung device? From a practical standpoint I feel the S5 is the better phone here. From an emotional standpoint I like how the HTC makes me feel.

Display:

I compared the displays VERY closely. The S5 wins on ALL fronts except one: Autobrightness. I had them side by side, the S5 shows much truer whites than the M8. The M8 at max brightness looks almost yellow. The S5 looks pure white. The screen is BIGGER on the S5 and isn't crowded with software buttons. I am simply not a fan of software buttons. I like tactile feel. The screen on the S5 can get VERY VERY dark, the M8 can't. The S5 AB is wonky, always a bit too dark. The M8 is always just a few steps brighter. This is always a plus except for at night.

Touchwiz vs Sense:

No preference.

How long will I keep the device:

I feel that the M8 will be gone in a year, because the M9 will have a better camera that make it a worthwhile upgrade. I can see myself holding onto the S5 for two years, it really is maxed out with specs and just works. On the other hand, the uninspiring nature of the S5 will probably make me want to ditch it in 2015.

Basic inputs:

It actually takes longer to use the M8 for basic inputs, turning the device on, and turning it off. The Samsung turns on a bit faster with just pushing the home button. Fingerprint scanner unlocks more quickly. Side power button is far superior.

Double tap on the M8 is NOT perfect. Neither is holding the device in landscape and hitting the volume key to activate the camera (doesn't work on the first try about 30%). Double tap takes you to the first lock screen. Then you have to slide the icon of what you want to use and input your pin. This can be mitigated by utilizing swipes instead of double tap. It's still not faster.

Buttons:

I often found myself constantly hunting for the onscreen buttons on the M8. The empty HTC bezel throws you off. It's very hard to have muscle memory when you have a big empty row where you think the buttons are. It also takes a moment for the buttons to simply appear. S5 doesn't have this issue due to the hardware home button.

Am I the only one that thinks it makes sense to have the back button on the right side like Samsung does it? I use the back button with my thumb 95% more than the current apps button. I don’t enjoy reaching across the screen on the M8.

Screen Off:

However often we turn the screen on, a lot of us are also turning it off. It takes longer to turn the screen off on the M8 than it does the S5. Every time I turned the M8 off with one hand it required maneuvering the device in a way that made me fear dropping it because the power button is on top and the device is long. I generally used my other hand to hit the power button just for that reason. That's not necessary on the S5.

Screen on with Music:

I LOVE the M8 speakers. I love playing music on this device around the house, while I'm in the shower, etc. If I am playing music on the M8 and have the device on the counter, and I want to change a song, it's not designed to register a doubletap when laying flat. With the S5, I hit the home button and it brings the screen up. It takes significantly longer to either find a way to hit the top power button or repeatedly tap the screen until it registers on the M8.

Speed and Lag:

In day to day use, after disabling bloat on the S5, the devices are equally as snappy. In fact, the S5 is more accessible for the reasons mentioned above. That's all that matters, because all of us here are capable of tinkering and optimizing.

Disable S-Voice, My Magazine, transitions, and go into developer mode and reduce animations to .5x, and trash/disable all the bloat in apps. The S5 has no lag at all once you do that. I know it's a PITA, and you shouldn't have to do that from factory, but just do it. You're on XDA, it's easy for you.

Everyone wants to talk about microseconds worth of lag, what about basic functions, like turning the screen off. The S5 is faster from a basic INPUT perspective. I think that matters a lot. It's little things like that, things I do often, which should be taken into consideration when you talk about how long you have to wait for things between devices. If we are going to argue about tenths of a second, these things matter.

Development:

Compare the # of posts in the M8 forum vs. S5 forum. Twice as many here. There will be more development and a bigger community on this device. I personally don't care about this at all. :)

Features:

With the S5, I won't ever use the fitness stuff on the device. I won't ever buy a gear fit watch (that's technically a feature). The main feature is the fingerprint scanner. Train it with one hand and your thumb to the side. Do three prints of just your thumb. It's then easy to unlock with one hand 90% of the time on the first swipe. It's very fast.

The M8 has much, much better speakers. If you use your device as a music player on a desk, around the house, in the bathroom, this matters. You can also activate the camera by tilting the device and hitting the volume button, this is a nice feature on the M8.

S5 water resistance is nice to me because I have a daughter, I live in Oregon (it rains), and I use my device in the bathroom (I know, gross).

Ergonomics:

I'm going to differentiate this from "AESTHETICS" for my opinion here. The S5 is easier to hold and issue inputs into for almost all purposes. It's lighter and requires far less movement with your hand. It has a "thumb mode" available through software which can shrink the screen size down.

The M8 is too long and doesn't have a power button available to easily press. It's much easier to keep a firm grip on the S5 than the M8. I was constantly in fear of dropping the M8.

From an aesthetics perspective, the M8 wins. It looks much, much nicer and just screams to be held. From a practical perspective, the S5 has better ergonomics.

My Recommendation:

If you care about features and functionality and ergonomics, take the S5. If you care about how a phone looks and makes you feel when holding it and having a mini-boombox, take the M8. If the camera is your only consideration, take the S5.