I believe it was Tech TV, but when the iPhone 4 first came out for Verizon, they did a side-by-side comparison of the AT&T model & the Verizon model in San Francisco. They went to various locations around San Francisco testing signal strength, web page load times, uploads/downloads, etc and I recall that all but 1 of the tests came out as Verizon being the winner.
As far as the Galaxy Nexus goes, obviously, you can acquire it for either service. The plus with Verizon is you get 32GB rather then 16GB, although the battery drain is faster(with LTE on) and I believe Verizon's plans are still the most expensive also. Personally, I'm only on Verizon because I've got the no-longer-offered 'unlimited data' otherwise I'd say bye and go to AT&T or T-Mobile. I kinda miss having a GSM phone due to the ease in phone swapping + worldwide functionality(switching to other providers).