At this point in time I would say that all those locos are very close
in quality. I'm speaking here about diesel (or non-steam) locos.
Kato used to be superior to all ther others but in the last few years
Kato's quality has gone down a bit while others almost caught up to
Basically Kato, Life-Like, Atlas and I think Model-Power and even
others are all using the same low-friction mechanism design. It was
originated by Kato but all the others copied it. Not sure about
Bahmann new diesels (haven't seen one yet).
While design is similar, the overall quality and tolerances of Kato is
still a bit better than the rest. But for all practical purposes, they
are all very good.
I'm especially impressed with Life-Like and Model Power quality. They
have become viable manufacturers of quality N scale locos (not just
cheap and poor running toy trains).