Odd that you mentioned TW.. I am an odd ball in that I like TW better than stock Android.. HTC Sense is horrid and Moto Blur or whatever they call it these days is even worse..I might be a bit naive in saying it's all about hardware. My personal preference when using Android is to go with stock Android. I was in a discussion with a Samsung rep on Twitter who said customers prefer TouchWhiz. I could be snarky and say that's because it looks like an iPhone, but perhaps there is some value add that I'm unaware of..
Choosing today, I think the HTC One X hardware is what I would opt for over the SIII.
One MAJOR advantage that the iPhone has, IMHO, is the lack of crapware and the lack of carrier and manufacture branding all over the device.. My Note for instance was LOADED with crapware & Samsung bloat. It had AT&T branded on the top front, Samsung branded on the bottom front and Galaxy Note on the battery cover.. I think all this branding takes away from the nice look that the Samsung devices could have..
Yes the bloat is easily removed / frozen with root and titanium but the ugly branding is there forever.. Imagine if the front of the iPhone said AT&T at the top and Apple at the bottom in big bold letters.. YUCK!