My reception on my GNex has been great since the JB update. If you have a Nexus 7 and an unlimited data plan, then you for sure want the GNex so you can tether the Nexus 7 to your GNex via WiFi for free.
I am unlocked and rooted and use Switchpro Widget to tether my laptop via WiFi. It is sooooo convenient!
The only downside to the GNex is the battery life, which unfortunately sucks. I have 2 extended batteries and a cradle charger so I have a backup battery if I use my phone a lot during the day. If I am in the car, I make sure to charge it while driving.
If you are going to get a case for your GNex, and I highly recommend that you do since it is a slippery little sucker, many cases don't fit the extended battery. The Diztronic does and it is my favorite.