I got the HTC One X the day it was released (due to the fact that I had been waiting for the Samsung Galaxy SIII after my Samsung Galaxy SI had come out of contract, and couldn't be bothered to wait around any longer) and I LOVE it.
I'm not going to compare it to the iPhone4S, because they're different beasts, and both Martin and DA have already outlined my opinion of them
I'm going to break is down to various areas and let you decide for yourself though:
Interface
The HTC Sense interface is so much nicer and intuitive that Samsung's TouchWiz (I know this from experience as I had rooted and flashed several ROMs on the SGS as I was bored of TouchWiz).
Size
I thought the HTX One X would be too big, but took the gamble, and although the screen is big, the outer casing isn't at all, and making it just the right size ( to the point that the off switch is on the top, and I can get my hand around the bottom and top of it to switch the screen on/off with one hand rather than needing two).
The design of the SGS3 however is very rounded at the top and base which adds extra size and unneeded bulk to it, which I really don't like about it.
Battery
Which the SGS3 on paper has the bigger (and therefore better) battery, the HTC One X (as well as being a quad core), actually has a 5th tiny core that is used when the phone is in stand-by, and uses next to no power, while still undertaking background syncing tasks, and has been given amazing reviews on that aspect of power management. Also, given I've had this for nearly 2 months now, on normal day-to-day usage it will last over a day. If I use it non-stop for several hours, then of course it will die quickly, but for normal use, it reserves power very well!
Processor / Performance
They both have quad core (albeit with the HTC One X having the 5th power saving core) with the HTC One X at 1.5Ghz, and SGS3 at 1.4Ghz - not much in it really.
That said, with regard to the benchmarks, none of them are accurate, because none of the benchmarking software does accurate testing for quad core multitasking, and only make use of dual core techniques - this is why the HTC One S is coming out better in some of the benchmarks than the X at the moment.
With regard to the HTC One X vs SGS3, the SGS3 will perform fractionally faster, due to TouchWiz being so very basic, and the Sense interface being slightly memory hungry, albeit the extra processor making it up a little, however to me that doesn't make up for the crappy interface of TouchWiz. So far, I've struggled to make my HTC One X lag at all, for anything other than high intensity flash webpages (the type that are laggy on a mid-spec PC anyway).
In terms of other features that really differentiate them:
- The screen quality is apparently cheaper on the SGS3 than the HTC One X, but no idea if that's noticable.
- The camera software of the HTC One X is amazing!
- The SGS3 has a SIRI type speech app (S-Voice) built in if you like that kinda thing.
- It also has a feature that meant to track your eyes and brighten/dim the screen when you look at it (kinda pointless if you ask me)
- HTC is better at rolling out phone updates than Samsung.
- Samsung's case is apparently a cheaper quality, and gone back to a similar style to the original SGS.
- HTC One X doesn't have separate SD card slot, but with 32Gb, why would you need one.
All in all - they're much of a much-ness, and the only thing separating them are the design of the case, and their own overlay on Android 4 (TouchWiz vs HTC Sense).
I prefer the HTC, but I'd say try them both out and see which you prefer.
Update:
For the size issue, have a look at this image to see the difference between the two in someone hand:
