Overall reviews look pretty close.

http://www.theverge.com/2012/5/25/3042640/samsung-galaxy-s-iii-review

http://www.theverge.com/2012/4/2/2919202/htc-one-x-review

Older pentile displays annoyed me, so I'd personally lean more towards the HTC. But I haven't seen a S III in person, so perhaps the pentile issue is hidden a bit more with the slightly higher density compared to my two older devices.