I just wrote about that here:
http://forums.androidcentral.com/go...wner-who-had-opportunity-switch-att-onex.html
Yes the One X has amazing hardware, but for me the Sense software totally turned me off. The screen is better but I think the difference is overblown. The only difference that I think is really noticable is the whites on the One X look really white where as the Gnex's superamoled doesn't give great whites or greys. The Gnex does have better blacks and excellent contrast although the One X contrast looks really very good too.
I am the type of person who is less interested in a feature list and more interested in a streamlined experience that just makes sense(no pun intended). ICS stock feels like it had a vision behind it. Sense just seems confused, but that is just my personal feelings.
If you don't mind rooting and putting custom software on the One X and voiding your warranty, by all means get that. But I think the stock ICS nexus with its better google support is enough to keep me in the nexus line.
Also I prefer the onscreen buttons, unlike many here. That is subjective, but I like the direction google is going with that and I want to support it.
I would take the One X over a Galaxy S III any day of the week also, not that that has anything to do with your question.