Well they should have picked someone other than LG. LG doesn't have that great of a track record at all. The phone is also uncomfortable to hold compared to the s3 and galaxy nexus.
Honestly the phone almost feels better in hand than the GS3. Not sure why everyone is saying it feels awkward. However, keep in mind LG makes the phone to Googles specifications. It's not the Optimus G to the T, but it's close. It is what it is for $300.
I have both and will sell one, I just can't make up my mind which one though.
But even after all that, I'd still recommend the GS3 based on battery and camera performance alone.
Is the battery on the GS3 significantly better than the Nexus 4? This has always been an issue with Android phones for me, iPhones always win for battery life.