Personally have an S3 but looking to grab either an S4 or One as sister needs a new phone but any of the newer stuff would be wasted on her
Going from the "extra" software features of the S3, I've had pretty much everything disabled from day one. This extends battery life, speeds up the phone somewhat and makes it feel less clunky. The only added software features of the S3 I've used are the multi window they added recently and the video popout, even they've been used sparsely. I get the feeling all of these features the S4 is touting are much the same; Samsung engineering flashy gestures which will find no use in daily life. There is not a single software feature I can see being useful.
I'm also tossing and turning on how much an issue the polycarbonate shell is. I've recently come in to contact with a lot
of phones on a weekly basis and I can't ignore the really great feeling of a metal chassis. Then again I've held the S3 for the past year and I've never felt like it was going to break. My only concern has been in taking the back cover off, which I rarely do but at least the S3/S4 permit it.
The One is a great looking phone, if only they'd also release it in darker colours. My main gripe with the One however, is the software on it. It seems a lot more restrictive than Sense used to be and the only reason I've stayed loyal to Android is the ability to tweak most everything without having to resort to rooting/jailbreaking, although doing either does open up far more options.
I'd also disagree with posters suggesting HTC don't know how to make an ergonomic phone, you only have to use your common sense to realise the ridiculousness of such a statement; peoples hands and the design of phones in the last few years alone are staggeringly varied. Personally I think the 8X is one of the nicest to hold in hand, I imagine the One will feel much more like the iPhone 5 though.
It seems that I will most likely have to custom rom whichever phone I do get, but battery and storage are what it comes down to in the end. I'm usually away from a power socket 14-18 hours of the day, if the battery life of either are good enough it should be less of a concern but I would enjoy the extra space on my phone very much. The lack of a replaceable battery and mSD card slot are what persuaded me from the One X to the S3 last year and I fear it will be a similar outcome this year. But let us wait until full reviews and demo units are available before we speculate too much.
Sorry for the epic post, thought opinions would be appreciated.