I still think iSmoothRun is easily the best run tracker app on the iPhone. The developer has put together a pretty good Watch app, given the limitations of Watch OS 1.0. But its only available to beta testers via TestFlight. He may still be adding users if you ask him (send a comment via the Feedback function in the iPhone app). I can only assume he will update it for watchOS 2 closer to official release.
What makes the iPhone app great is the customizable screens, the cadence tracking, and the ability to export to many and multiple sites automatically (i.e. Run keeper, MapMyRun, Nike, etc.). Also tracks shoe mileage (for multiple pairs of shoes).
What makes the Watch app great is that all the stats are customizable in 2 swipe-capable panels. You pick which 3+3 metrics you care about. It changes color when paused.