Sound quality of mixing in Protools vs others..Discuss

I would like to hear from anyone with first hand knowledge or working with someone with first hand knowledge on the quality between Protools and other software when mixing (i.e Cubase or Nueudo). I have had a couple of major engineers telling me they move their sessions to different software to mix on (if it’s in-the-box) because it sounds better. While I haven’t purchased either one to run my own tests yet, I am interested to hear from some people who maybe doing this. Thanks.