Update: For a deeper dive on these two, we've run our hands-on look at these two phones.
The phones' dimensions aren't dramatically different, but the HTC One (M8) is three percent longer, three percent narrower, and 16 percent thicker than the Galaxy S5.
The Galaxy S5 is nine percent lighter than the One M8. That probably has a lot to do with this next category ...
I admit having a soft spot for Samsung's pleather. It's light, I think it looks pretty good, and it's comfortable in hand. But there's no question that the prize for premium, high-end design goes to HTC. The One M8 has a unibody aluminum finish that looks stunning. This is the BMW of smartphones.
We have three color options for the One M8 and four for the GS5.
The Galaxy S5 gives you four percent more screen real estate than the One M8. And in most apps, the actual difference will be a little bigger than that. That's because the One M8 uses onscreen navigation buttons, while the GS5 has physical and capacitive buttons below the screen. You will, however, get the One's full 5-in landscape in areas like your image gallery, videos, and Google Play Books – thanks to Android's Immersive Mode.
Both handsets have 1080p screens and look plenty sharp.
The HTC One M8's Motion Launch is a set of sensor-based shortcuts. When you're holding the One in portrait mode, you can jump straight to your lock screen, home screen, or widgets by swiping or tapping the screen while it's off. You can also do things like activate the camera by pressing the volume button (while holding it in landscape mode) or answer a call by lifting the phone to your ear.
Heart rate sensor
Samsung is trying to get a jump on mobile fitness tech with a pulse sensor in the GS5. It sits below the phone's rear camera.
Never one to let the iPhone hog the spotlight, the Galaxy S5 has its own fingerprint scanner. Unlike the one in the 5s, though, you have to swipe your finger down from the bottom of the screen, rather than just rest it on the home button.
Internal storage options are the same, and this year HTC also threw in a micro SD card slot. Those are nothing new for Galaxy flagships.
It's too early to jump to conclusions about the GS5's battery life, but the One M8 is going to be hard to beat. In our standard test, where we stream video with brightness set at 75 percent, it lasted an insane nine hours and 20 minutes.
Ultra/Extreme Power Saving Mode
Both phones have similar features that let you squeeze out some extra battery life at the end of the day. Their displays will shift to black & white and the phones will limit which apps and processes can use resources. When these modes kick in, you'll be able to get hours out of just a very small amount of juice.
There is one catch though: the Galaxy S5 ships with this feature, but the One M8 will be getting its version in a future software update.
Looking just at megapixels, this looks like a blowout for the Galaxy S5. But the One's camera has bigger pixels ("UltraPixels"), which help it take brighter and more colorful shots under poorly-lit conditions. Consider this one an incomplete until we test the GS5's camera.
The One M8 also has a second camera devoted to sensing depth. This lets you create blurred-background shots (Bokeh), where you can choose the point of focus after you've already snapped the picture. The GS5 has a similar (software-based) version of that same feature, even though the phone doesn't have any depth-sensing hardware.
Both phones will let you capture Junior's Little League home run or Fido's frisbee trick in slow-motion.
Last year Samsung marketed a separate version of the Galaxy S4, the GS4 Active, that had some water and dust resistance on board. This year the Galaxy S5 has the same protection built-in.
Speakers might not be the first thing you're looking for in a new phone, but good luck finding one with better audio than the One M8's front-facing BoomSound speakers. It produces the best sound I've heard from any smartphone speakers.
Both phones ship with the blazing-fast Qualcomm Snapdragon 801 processor. Performance isn't an issue with the One, and it shouldn't be with the GS5 either.
As is usually the case with Samsung flagships, non-LTE markets will see an octa-core Samsung Exynos chip in place of the Snapdragon.
2 GB of RAM in each handset.
Both devices are shipping with the latest version of Android. You also have a custom UI, either HTC's Sense 6 or Samsung's TouchWiz, sitting on top.
HTC dropped a bomb on us by releasing the One M8 just an hour after its launch presentation ended. The Galaxy S5 launches on April 11, though you might want to double-check whether your country and carrier are getting it on that day.
Starting price (off-contract)
The price we're seeing most often is US$650 without a contract for either phone. And US carriers are typically pricing them each at $200 with a new two-year blood oath.
This is, of course, just a quick features and specs-based look at these two flagships. We'll have much more on both of them later on, including a hands-on comparison. In the meantime, you can hit up our HTC One (M8) review for more on what might just be the best smartphone around.