[T-Mobile Samsung Galaxy S 4] hoevito:
I've had a similar and also slightly different experience. I also came from an HTC Sensation which I've had for about 2 years, previously owned the og Galaxy S (Vibrant), and instead of the S4 I chose the HTC one, and got the GS4 for my wife instead.

Here are my observations since I actually have both phones and can compare them with NO bias...

-A lot of the online mainstream reviews you'll read between the two hit the nail on the head. The One imo is a better "phone". It does indeed have less features then the S4 (although many of them are gimmicks like the eye scrolling/tracking, airview, and a few others) but the speakers are far superior, which obviously aids for anyone who ever uses speakerphone or plays music and videos, the call quality is also a little better, the phone is more fluid and faster than the GS4 with basic functions like scrolling screens etc, and the phone of course has a MUCH more "premium" feel. Sense 5 is MUUUUUCH better than past versions of Sense and like a lot of review say, it *DOES* improve over stock android in actual useful features. The look is subjective of course but it's flat, useful and fast, and to me that's all that matters. The camera is better than any past smartphone I've ever used (Tmobile Dash>G1>Vibrant>Sensation>One) so I like it personally, but compared to its rivals like the GS4 I guess it's not the best, but does everything I've ever asked of it VERY well so no complaints from me.

The GS4 on the other hand has a superior camera. The camera on the One isn't bad at all, and kills the Gs4 in low light conditions and the aspect ratio and wide lense captures waaay more in each frame, but the GS4 has more camera features, packs a crapload more detail in each shot, has some pretty useful camera modes the One doesn't have, and is just generally better. The Galaxy might not be made of aluminum like the one, but it's lighter and imo actually feels better in my hand (without a case). Once you add a case in the mix, hand feel is null and void obviously but if you like to go commando the Gs4 feels better and will probably hold up to abuse better than the One due to the polycarbonate body and gorilla glass 3. The screen on the Galaxy is bigger than the One while the actual phone altogether is lighter and smaller so that's pretty nice, but it's not really THAT noticeable to be honest. One huge, huge advantage the Galaxy has over the One is removable storage and battery, which *USED* to be a deal breaker for me back in the day, but I've learned to live without them since I got my One, so either way it's a definite advantage but I guess how much so is up to the user. The Galaxy also has native quick settings built in which the one doesn't have (yet), so minor issue but another positive for the galaxy.

As far as negative for each, I'm actually on my second One already. Somehow my camera lense glass cracked even though I keep the phone in case and have never dropped it or bumped it. It just appeared one day in addition to the top speaker grill starting to separate from the body. Weird, but I got it replaced and the replacement is doing fine and actually stands up to overclocking and undervolting better than my old unit, so that made me pretty happy lol. That's really the only issue I've had with mine, but on the whole, the phone is definitely more fragile than the Galaxy WITHOUT a case. It scratches easier, dents, chips, etc...while the Galaxy doesn't.

The Galaxy feels better in hand (caseless) than the One, but it's slippery as hell and slides around easily and can be more prone to being dropped. Again, only an issue without a case, but this is my observation.

Touchwiz...personally I think it's a mess. I don't care for the look, as many have said it feels like your still running Gingerbread 2.3. The look hasn't changed much since I had a Vibrant running Touchwiz from 3 years ago, and while Touchwiz DOES have some unique features and generally does more than Sense and stock android...it's just ugly as hell while doing so lol. The Galaxy also does feel a tad slower and microstutters every so often while the One is almost always fluid and seems much smoother even tho it's running a newer version of android and has slightly better specs on hardware...it just doesn't "feel" like it. Other than that it's a fantastic phone and we haven't had any problems with it whatsoever unlike the One.

Between the two...if I just had to pick one, it's a toss up. I prefer my One honestly but I can see the advantages of the Galaxy S4 with it having more features so I'll just break it down like this...

Usefuleness as an actual phone

One>S4

Camera

GS4>One

In hand feel, portability

One=GS4

Usefulness as a multimedia device

GS4=One

Expandability

GS4>One

I will say that between the two if this even matters to anyone...I get WAAAAAY more props and questions and even jealous stares directed towards the One lol...