Is: they fewer junk, throwaway episodes. Voyager had a few good ones, TNG had many like DS9. Still, the former had many, many, many very forgettable and dare I say many terrible episodes.
Seriously, I can count on 1 hand DS9's junk eps. I would need more phalanges to get Voyager and TNG (and TOS)
While I love DS9, I can count rather more junk episodes than that, mostly in the final season, between horrid shit like "Take Me Out to the Holosuite," and pretty much every episode involving Ezri Dax.