Samsung and HTC set out on different paths from the very drawing board. Samsung focused on sensible finish and practical build, while HTC wanted a design that makes a statement.
In the end, the Samsung Galaxy S4 uses a plastic body with a Hyperglaze finish just like that of its predecessor. Taking after a design that wasn't too widely loved in the first place is a bit of a turnoff to be honest, but the slimmer waistline and thinner bezels still make the Galaxy S4 look much better than its predecessor (which is larger, despite the smaller screen). The Galaxy S4 is actually more compact than the HTC One as well, but the difference is negligible - at least until you account for the fact that the Samsung fits a bigger screen.
The plastic build has a number of practical advantages - it's lighter for one, 20g, and the removable back cover means a user-replaceable battery and a microSD card slot.
HTC developed a complicated process of carving the One out of a block of aluminum and the result is arguably the best looking smartphone to date. The phone is a bit thicker than the Galaxy S4, but the curve of the back hides that very well. The extra weight and the aluminum finish give the HTC One a premium feel that really puts its competitor today to shame, though.
Even if you don't care about the exact numbers, the differences you're likely to notice are that the Galaxy S4 is thinner, lighter and has a bigger screen compared to the HTC One.
On the other hand, a 4.7" screen was a conscious choice by HTC (as something more manageable) and the front-facing stereo speakers are a great touch. We're not sure about removing the third button though, whether it's Menu or App switcher, physical or on-screen, a third button is practically expected out of Android phones. The duties of the missing task switcher key on the One have been taken over by the home key, but that's its third function and that makes it a bit unintuitive.
With an IR emitter on the top, both phones can control appliances at home - TVs, set-tops, air conditioners and so on. On the HTC One, the emitter is built into the Power/Lock key, which isn't a problem, but the button itself is small and flush against the surface, making it difficult to use. The volume rocker isn't much better.
Samsung kept the IR emitter separate on the Galaxy S4 and put the Power/Lock key in the traditional spot on the right, which benefits single-handed use. It helps that the button is properly raised too.
Winner: Tie. This is by no means a goalless draw, though - From a pure design standpoint, the HTC One wipes the floor with the Samsung Galaxy S4. The One is the phone to be seen with, it looks more expensive if you will. The Galaxy S4 on the other hand is deliberately underplaying the looks - as if to say that what matters is on the inside.
The best thing about the Samsung Galaxy S4 hardware is that the smartphone is more compact while offering a bigger screen and a larger battery. But it just looks boring, a minor update of the Galaxy S III design, which we didn't love in the first place.
The HTC One on the other hand looks and feels great. With 32GB of built-in storage (there's a 64GB version too), we didn't miss the microSD card slot much either. The speakers are definitely a plus.
Yet, a card slot (more than just memory expansion) and a removable battery (easy to throw in a spare, or replace a defective unit) are important to many users and help the Samsung Galaxy S4 clinch a hard-fought draw.