I've got a One X and my missus got her S3 today, there is very little between the phones... some of the things you say are much better are barely noticeable unless you test in a lab... I'm not an HTC snob it's the first one I've had but I'm interested in whether those results are taken with the massive firmware improvements (to the tegra 3 version) as they have really improved the performance of many features of the phone.
The camera on the One X is better than the S3 except in low light, the S3 is much better with the bad light pictures but after some testing myself today in sunlight or normal inside-the-house light the one X just looks that little more vivid and warm. In low light the One X tends to get a yellow hue to the pics.
I would also say the screen is much better on the One X, again it just has that bit more warmth to it and I don't know much about fps but it takes perfect videos... very little difference between the two.
The build quality is decent on both phones, the S3 looks much better in real life than in the pictures of it but it isn't as nice looking as the One X... the brushed effect is there because without it the phone would look cheaply made.
The S3 definitely has a faster browser, a good second quicker using wifi (we don't have 4G in the UK yet so cant comment)
Both have a very smooth UI, samsung just edges it but seriously, there is very little between them. The thing the S3 absolutely kills the One X on is the removable battery.. I'm not bothered about the SD card but you need a spare battery.