I have been using an international HTC One X for a couple days now on ATT(works with 3G and "4g"). I sold my iPhone 4 in anticipation of the iPhone 5 coming out. I just started doing android development(was and will continue to do iOS dev too) at work so I am using a test phone as my daily phone.
This is probably the best android phone I have ever used. I used a samsung captivate for a couple months because I dropped my original iPhone 4 in a lake. I didn't think android was polished enough.
This phone is pretty fast, not really any lag that I can see. In fact it seems to preform better than the SG3 that we have (also an international model). I am using the stock 4.0.4 rom w/ HTC 4.1
We could argue for a while about the merits of android, but in terms of hardware, things I don't like:
1)I miss having a dedicated mute switch.
2)I actually don't care for the notification LED, its distracting when watching movies and such
3)Most of the time when I palm the phone, I can't press the lock button to unlock/lock the screen with one hand. I guess my hands are too small, because its awkward to try and reach it.
4) I wish the USB port was on the bottom
5) Not a fan of rear speakers on phones