I currently work for Rancher. I've also been building Internet infrastructure since 1996 and owned an MSP for 14 years that built and managed Internet datacenters for large US media companies. I've been working with containers since 2014, and since then I've tried pretty much everything that exists for managing containers and Kubernetes.
"The deciding factor" varies by individual and organization. Many companies use OpenShift. Many companies use Rancher. Many companies use something else, and everyone will defend their solution because it fits their needs, or because of the psychological principle of consistency, which states that because we chose to walk a certain path, that path must be correct. More specifically, the parameters around the solution we chose must be what we need because that was the choice we made.
Red Hat's approach to Kubernetes management comes from OpenShift being a PaaS before it was ever a Kubernetes solution. By virtue of being a PaaS, it is opinionated, which means it's going to be prescriptive about what you can do and how you can do it. For many people, this is a great solution -- they avoid the "analysis paralysis" that comes from having too many choices available to them.
Rancher's approach to Kubernetes management comes from a desire to integrate cloud native tooling into a modular platform that still lets you choose what to do. Much like Kubernetes itself, it doesn't tell you how to do it, but rather gives fast access to the tooling to do whatever you want to do.
Red Hat's approach is to create large K8s clusters and manage them independently.
Rancher's approach is to unify thousands of clusters into a single management control plane.
Because Rancher is designed for multi-cluster management, it applies global configuration where it benefits the operator (such as authentication and identity management) but keeps tight controls on individual clusters and namespaces within them.
Within the security boundaries Rancher gives developers access to clusters and namespaces, easy app deployment, monitoring and metrics, service mesh, and access to Kubernetes features without having to go and learn all about Kubernetes first.
But wait! Doesn't OpenShift give developers those things too?
Yes, but often with Red Hat-branded solutions that are modified versions of open source software. Rancher always deploys unadulterated versions of upstream software and adds management value to it from the outside.
The skills you learn using software with Rancher will transfer to using that same software anywhere else. That's not always the case with skills you learn while using OpenShift.
There are a lot of things in Kubernetes that are onerous to configure, independent of the value of using the thing itself. It's easy to spend more time fussing around with Kubernetes than you do using it, and Rancher wants to narrow that gap without compromising your freedom of choice.
What is it that you want to do, not only now, but in the future? You say that you already know Kubernetes, but something has you seeking a management solution for your K8s clusters. What are your criteria for success?
No one can tell you what you need to be successful. Not me, not Red Hat, not Rancher.
I chose to use Rancher and to work there because I believe that they are empowering developers and operators to hit the ground running with Kubernetes. Everything that Rancher produces is free and open source, and although they're a business, the vast majority of Rancher deployments make no money for Rancher.
This forces Rancher to create a product that has true value, not a product that they can convince other people to buy.
The proof is in the deployments - Red Hat has roughly 1,000 OpenShift customers, which means roughly 1,000 OpenShift deployments. Rancher has fewer paying customers than Red Hat, but Rancher has over 30,000 deployments that we know about.
You can be up and running with Rancher in under ten minutes, and you can import the clusters you already have and start working with them a few minutes later. Why not just take it for a spin and see if you like it?
I also invite you to join the Rancher Users slack. There you will not only find a community of Rancher users, but you will be able to find other people who compared Rancher and OpenShift and chose Rancher. They will be happy to help you with information that will lead you to feel confident about whatever choice you make.