My £0.02 is that Kubernetes has the backing of Google who have a tremendous amount of experience with container orchestration. And while using Kubernetes it really shows, things are pretty well thought out, lots of features out of the box etc.

With docker swarm it's taken them this long to get simple secrets integrated, and as with all of my experiences with first party docker tools: they seem ok at first, but the devil (and problems) are in the details.

I trust Google more to get this right, and I highly doubt Kubernetes is going anywhere.