With the newest wave of Android phones, either both of these phones will "wow!" you or neither of them will.
Both will make calls on America's greatest network. Both have smooth and responsive web browsing on unnecessarily fast LTE connections. Both have admirable processing power--enough to multitask with minimal stutter. Neither of them have an innovation that is groundbreaking. For me, it really came down to two things
1. Physical looks
RAZR: "blocky" look. Premium materials. Thin and sleek.
Nexus: curved, rounded look. reinforced plastic.
For me, I prefer the GN. I really like the curved design, and coming form a DX I think I'm a bit bored of the Moto designs. The plastic isn't that much of a deal to me--I'll have my phone in some plastic or synthetic case either way--no amount of kevlar will assure me that it's safe from drops. Honestly, most negative reviews complain about the plasticky feel. Both phones will have dents/scratches if you drop it. Just because the Nexus is made of plastic doesn't necessarily means its not as durable--it just means it has that cheaper feel, which some people don't like.
2. Software
RAZR: BLUR, smart actions, Motocast, etc
Nexus: ICS
Coming from a DX, I will say that I absolutely hated their older versions of BLUR, mostly because it was slow.
But with the newer D3, Bionic, etc, the launchers are much smoother. Some of the widgets are super slick (quick contacts) and BLUR reminds me of that modern blocky/tile feel that you get with Windows phones. Smart actions is like a steroids version of their battery manager, but it isn't anything that hasn't been done before.
With ICS, you get a blank canvas. If you look at any youtube review, you'll see that the stock screens from the launcher are all disoriented--clocks here, widgets there, etc--whereas on the Moto demonstrations everything's organized and looks very appealing, with social widgets on one screen, media widgets on another, etc.
Having used a DX though, I've found that the "features" I loved that Moto or HTC offered exclusively (Sense widgets, quick contacts, etc) could be replicated in function by 3rd party apps (and most of the time, in aesthetics too!). Eventually, I found myself dying for CM7, because I just wanted raw speed. All of the extras that BLUR offered I either didn't need, or could find something else to replace it.
For me, BLUR/Sense/TW wants to dictate how I use the phone, but I'd rather spend the time customizing my phone so that it fits my needs. The whole freedom of Android is that all the APIs available to Motorola, Samsung, LG, etc, are available to everyone. Things like "smart actions" aren't really appealing to me, because apps like JuiceDefender can emulate its functionality (and in theory, I could make a similar app).
This is why I'm ultimately going to get a Nexus. I found myself spending more time customizing my Moto phone to look and run like stock android than being satisfied with what BLUR offered me.
Plus, the new APIs from 4.0 will allow for things like creating calendar events by voice, transferring data with NFC, etc. They're not groundbreaking by any means, but they have the potential to be very convenient for my everyday needs. I know that the RAZR will get ICS soon, but when I desperately waited for GB on my DX the BLUR'd version didn't live up to my expectations.
Most people don't really care about the things that factored into my decision. If you take the time to thing about how you want to use your phone, what you want it to look like, how much time you're willing to spend customizing it, then I think you'll have a much easier time choosing a phone than if somebody else shoved specs and their own user experiences down your throat.
Both are awesome phones, but for the way I play with Android, there's no doubt as to which I'm going to get.