Ok, so I looked:
Hazard played 19 times against United, scoring 5 and assisting 2. In those 19 games, Chelsea won 8 times.
Salah, in 12 games against United has 12 goals and 4 assists. In those 12 games, Liverpool won 6 times.
I'm not a stats person, I only looked it up for my own curiosity. It does, however, paint a picture of Salah being more dominant, by every metric. If Chelsea would have won say 12 or 13 of those games, you could say that goals and assists don't paint a full picture. They didn't though, and this includes times when Chelsea were challenging on all fronts. Honestly, other than personal preference, I can't see how Hazard is better in any way.