Would love to hear from someone who has used both though.

I've never seen an excellent, detailed comparison actually, as conversation on the subject tends to devolve into a "discussion" on ethics. Meaning, people who dislike GNU or GPL or Lisps or something get testy and argue uncharitably (imho, please prove me wrong, not flaming here, etc).

This is ironic, to say the least, as one of the main points of the proponents of the "anti-GNU" side tends to be how Guix is too opinionated and pushy and hard-line etc. So we've a classic upside-down situation, which is a real shame, as Guix seems to be in reality a practical project with lovely people involved that's doing very interesting work.