The Apple Watch smokes the competition in nearly every category, and I can say this while being 100% serious. I have used Android Wear, Pebble OS, and watchOS extensively within the last year and watchOS is the most refined, consistent, and has the best app support and ecosystem of all the platforms. Android Wear is very beta feeling, with lots of stuttering and lag couples with random rebooting. The Pebble is very good (a very close second to the Apple Watch) but is nowhere near as feature rich as the Apple Watch.
Once watchOS 3 comes out, I don't think any other watch will be able to compare in terms of speed, reliability, or refinement. I'd say watchOS 3 is pretty revolutionary