[T-Mobile Samsung Galaxy S 5] crazeco:
:laugh: I had just made a post in the HTC forum, I figured it was a good response to your question!

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. :)

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.

Lag:

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. The other reasons I mentioned in my previous post are all equally applicable here. The device is faster from a basic INPUT perspective. I think that matters a lot.

Features:

They are both android phones. Software they are identical IMO. 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.

The camera software on the M8 is better. The camera itself is not. 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:

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.