It really just boils down to what you really want.
Galaxy Nexus is a pure vanilla form of Google Android 4.0. It is very well designed to be a Development phone. So there are options on the phone that you won't get with any other phone that gets updated to 4.0 ICS. I'm not sure if the Nexus S has the same Developer options. And what I mean is, things such as Show CPU usage, Show touches, show screen updates, pointer location, etc. I'm sure you can get those features with a rooted custom rom phone. But stock Galaxy Nexus already contains these options. So you don't have to fiddle around to enable it. On top of that, it has Super AMOLED HD (720p) display at a 720x1186 2.0 scalability. It has an HD front camera and full HD back camera. 5 MP back camera is pretty low quality, but zero shutter speed is amazing for those photos you need to get at the right moment.
Razr will probably not contain those exact features when it gets upgraded to 4.0. But for overall quality, the Razr Maxx is where it is at. If you're not looking to develop on android, then maybe the Razr is where you want to be at. The radio is amazing, and the call quality is quite nice. The Camera on the Razr Maxx can't be beat with 8 MP and the video recording is truly amazing. The battery life is going to be where the Maxx takes a clear victory over the Nexus. I've had almost 48 hours of no charge on the Maxx with normal usage. Albeit, Juice Defender helps out with that big time. I'm not a big fan of Motoblur, not going to lie, and there is a ton of bloatware to deal with on the Razr, but nothing that a simple root can take care of. I think ICS will work wonderful on it once released.
Between the two, I like the fact that the Nexus is pure vanilla, so I'll take that gladly over the Razr because I'm a developer and need some of those advanced features. Not only that, most applications will run more on the Nexus vs. the Razr because of the fact that it is a dev phone.
Hope this helps out with your decision making.
Thanks.