They both server different wants. Personally, the iPhone is to small for me and I don't like how IOS does some things things, like no app drawer, it just puts all your apps on the screen. I also drop my phone quite often and I don't like using cases, so iPhone would be out for me. If you are with VZW, you can only use the CDMA/LTE version, not the one Google is selling directly. Both phones have great features, go to the store and look at both. See which one you like better.
I can't tell you what to do, but I can tell you what I did. I bought my GNex outright as soon as the price dropped to 399 and I've been laughing for the past two weeks. I got the GSM one because there's always a carrier anywhere in the world that can handle it (i.e. for travel). T-Mobile also has some great plans if you own your own phone. Finally, I got a screen protector for my phone, I got Ghost Armor because of the kiosk that sells is nearby, but XOSkins has amazing customer service from what I've read on XDA developers.
Oh, and I bootloader unlocked, rooted, and replaced the ROM on my with AOKP within a few hours of owning the phone. Freaking awesome.