Having moved from Mesos to Kubernetes, Kubernetes just felt more mature. Working solutions for stateful sets, service discovery with DNS, flexible scheduling with affinity and tolerance, saner resource limits, a good CLI tool.
It's not a completely fair comparison since we also were able to offload persistent storage to Google Cloud, which is one of the harder problems IMO.
I think Mesos has improved since then, but it always felt like they were a bit behind.
In general Kubernetes feels like it is designed by people with relevant experience. Especially compared to our earlier experiments with Docker Compose files. People are praising their simplicity, but they left us solving a lot of hard problems that Kubernetes solves for us better than we could have done.
