Jekins is the incumbent option, not to mention, open source. GoCD is also open source and supports Kubernetes and can be installed with Helm Charts.

GoCD provides its core value out of the box. Maybe you will add a few integration plugins to make GoCD fit better in your environment. Jenkins will require many plugins to deliver value. You will need to understand the plugins, how they interoperate, and how to upgrade them. GoCD will feel more stable. Jenkins will feel more hackable. Which is a better match to your needs and philosophy?

Learn how to setup your first pipeline, or check out their enterprise plugins and support.