I'm going to put my bitterness aside for the moment (As far as I'm concerned, LG dropped the ball with regards to availability) and try to answer objectively...
There are really only 2 reasons to pass over the Nexus 4. If you need/want LTE or an SD slot. Sure the latest and greatest updates directly from Google is something everybody wants, however it's not always what it's cracked up to be. Case in point, the 4.2.2 update removes the ability to hack/enable LTE on the Nexus 4. I have no doubt someone will find a way to enable it again, but it was only half-assed anyway. I certainly understand not everyone is capable of getting LTE, but if you are...it's rather silly not to utilize it. I wouldn't purchase a phone not capable of utilizing everything I'm paying for through my carrier.
Putting all of the above on the back burner, with custom ROM's and the popularity of the Galaxy line, the fact that the Nexus' receive updates directly from Google is only a horribly minor benefit. Heck, I could download a custom ROM built from 4.2.2 for my S3 before it was even pushed to the Nexus devices! Most custom ROM's are also highly optimized for their specific devices.
The Nexus devices and the Galaxy series (with and without custom ROM's) are pretty much neck and neck when you ignore some of the above. I would recommend going for the one that you find most appealing with regards to look and functionality (ie. LTE capabilities, SD slot etc). At this point in time, nearly all high end devices have access to latest and greatest Google. Plus whatever other fantastic features custom ROM's bring to the table.
Edit: Oh and
Wait for the S4