The best editors provide finer granularity without sacrificing usability, make it easier to understand the effects of edits with before/after comparisons, and maximize the photo without hiding necessary controls.
They also need to produce good-looking results and be able to effectively correct problems in your original photos. But just having a lot of adjustments isn’t enough.
Generally speaking, the more options an editor provides, the more we like it-as long as the interface doesn’t get too cluttered. The best go further to offer stuff like healing brushes, a histogram, curves, split toning, layers and masks, correction for chromatic aberration, and more.