The consensus is that Grimm's law occurs before Verner's law. You will in the field of Indo-European linguistics always find someone who claims the opposite of what the consensus says. So it's important to know what the consensus is.
Here's an argument in favor of the traditional approach:
Verner's law turns voiceless fricatives into voiced fricatives. You can read more about that in my 2011 paper "The phonetics and phonologization of Verner’s law". But, Verner's law also targets Proto-Indo-European */k/. How is that possible? Well, Grimm's law turns Proto-Indo-European */k/ into a voiceless fricative */χ/, so if we order Grimm's law before Verner's law, then the outcome follows: */k/ > */χ/ > */ɣ/. You can read more about that in my 2009 paper "The development of voiced labiovelars in Germanic". My papers are here: http://folk.uio.no/sverrej/
I would like to know how those people who order these laws differently will explain these facts.