[HTC One X] greyhulk:
Don't flame. This is a constructive thread for those considering the GS3. I had both the International and AT&T versions of the HTC One X. Below, I'm going to list the benefits/disadvantages of both from my perspective. Hopefully this will help those of you who are on the fence about this.

HTC One X

Issues

Multitasking - No need to beat this to death. It simply didn't work as expected and while not a deal-breaker, it was very annoying, especially after going back to a phone where it works normally.

Bluetooth - I had all kinds of Bluetooth issues, from the connection to my car stereo, to others you have read about in the forums. I could live with most of them, but, again, annoying.

Exchange E-mail issues - Periodically, the mail app would just stop receiving exchange mail from both of my exchange accounts. It's like it would go to sleep and not wake up until I manually refreshed. Both the AT&T model and the International model did this. It was very frustrating, and kind of a deal-breaker on a smartphone for me.

Power button - Minor niggle, but I hated the placement of the power button and it was recessed a little far for my liking.

Battery - My battery life was okay, but not great. I was expecting miracles based on the battery tests, but my experience was that it was much less. I could make it thorugh a day with light-medium use, but just barely. I'm honestly not sure whether the Tegra or S4 did better. The S4 seemed to last longer with use, where the Tegra had better idle time.

Positives

The Screen - While I don't have any issue with the GS3's screen, the One X is just that much better. The SLCD2 screen is just that good.

Sense - Love it or hate it, I liked the optimizations that Sense added. Especially the social integration and the direct plugins to Dropbox and, on the International version, Skydrive. I will sincerely miss those.

Look and Feel - The One X was a good-looking phone and felt solid.

Camera - The GS3 camera app is okay, but the One X was definitely better with respect to burst mode and shutter speed. Not having to switch to a special mode for burst is priceless and the GS3 takes a few seconds to focus sometimes, where the One X did not. That being said, I think picture quality is better on the GS3.

Galaxy S III

I'll be the first to admit that I initially had no interest in the GS3. It looked like a barely better Nexus to me when they first showed it off. But then I got my hands on one.

Issues

Camera shortcuts - When you set up shortcuts in the camera app, they don't stay. Kind of defeats the purpose. The Galaxy Note had the same issue, so it seems to be something Samsung just hasn't fixed.

Seriously, that's it (so far). I have tested the hell out of the International version and have an AT&T version coming next week. I have yet to find any other faults or issues with this phone. Build quality is subjective.

Positives

Power button - minor, but I like the way the power button feels and it's easier to access with the index finger with one hand on this phone.

Face Stay - Seriously, how did I ever live without this? I hate when the screen dims while I'm reading. Face Stay works really well.

Dedicated menu button - This will matter less as time goes on and developers update their apps, but you get all of your screen real estate right now because there isn't a strip being taken up by that legacy menu button.

Notification light - The one on the HTC was rather dim and hard to see. In addition, it would stop blinking after a predetermined amount of time. The GS3 has a much better notification light, much like the one on the Galaxy Nexus.

Battery Life - Has been superb for me. Granted, it is much larger, but it doesn't make the phone heavy, so the more the merrier. It easily beats out both of my One Xs in battery life. I can't wait to see how the S4 model does.

Everything just works - This is something I took for granted with the One X. I wanted to keep it so bad, that I started making compromises and "living with" the issues it had. On the GS3, I have no bluetooth issues. I can stream Slacker in the background without it dying. Multitasking works great, and everything just works as expected (and intended), including exchange mail.

Bluetooth Voice Dialing - This was taken off of the One X for some reason, but I'm happy to report that it works and works well on the GS3.

Ultimately, both are great phones. Having used both (and variants of both) for several months, these are my impressions. Your mileage may vary, but I hope this helps any of you who are on the fence about which one to get or whether to change phones.