The fact is that whatever phone you buy, a better one will be released soon enough afterwards that you'll wonder if you should have waited - but if you play that game, you end up waiting forever. Which is why I don't have a tablet yet.
With the One X, to some extent I think it depends on how much you like HTC Sense. The SGS3 might well have better specs, but I like Sense, so I wanted to stick with HTC.
I've only had it 2 days, so it's difficult to give a detailed opinion. But I like the feel of the phone, external build quality seems good, the screen is fantastic, and Sense 4.0 is a major improvement over previous versions. My only concern is the lack of a microSD card, but in all honesty I rarely filled up the 32GB card I had in my DHD, so I'm hoping that won't be an issue. The only issues I've seen so far are all software, and updates will come.
I haven't unlocked and rooted yet, as I have a 14 day cooling off period to see if I'll keep it or not. But early signs are that I will.