I think I can speak frely and with some accuracy here.. I have (and they are both active and operational) the Bionic and the Gnex. I bought the Gnex cause I felt it to be the second coming of the D1.. and, so far, this is a very true statement. We here, like things to be unlocked and rooted and the Gnex gives you that.
Comparing thw two at physical value, I like the weight of the Gnex better and i like the screen better. I like the look and feel of the Bionic better. Dev wise though, there is no comparison. The Gnex has more ROM's than the Bionic and its been out way less time. An unlocked bootloader says it all. If you think the Gnex is lacking something, a dev will fix it. Because, on this phone, they can.
All I can say is, Gnex vs Bionic, .... Gnex without 1 second of hesitation. If I were a regular guy who didnt root and rom my phone and didnt care about bloatware and whatnot.. id stick with the Bionic no questions asked. But, I am a ROM'er and rooter and themer and, because of that, I will go Gnex til I die (or until the 3rd coming comes along in 2 years)