I'd rather buy the GS3 because it has the 2gb ram chip. That would allow you to run some damn good games and some pretty smooth multitasking. I'm a fan of the deep blacks in Samsung's amoled screens and they make dark Holo themes looks pretty slick.
Other than these 2 reasons I don't see a huge difference between the two devices since they both have Krait S4 processors, pretty large screens, removable batteries, and you can't expect either to have speedy updates past ICS on Sprint. I would end up running AOSP rooms on either device but HTC Sense does seem to be more lightweight and it's less heavily skinned compared to TouchWiz.
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