The more the merrier, I guess. I've always been comfortable using kubectl. The only UI I am forced to use is the Google Cloud Console one. Which is ok. For newcomers I would recommend using the cli tooling and dive as deep as you can before you zoom back out. If you run k8s, then you are probably big enough a company that you have prometheus or something like that which collects metrics for cpu/ram usage.
From a Developers POV it's definitely easier to interact with a GUI.. and I '+1' on what u/rhacker said: the best UI in that case is probably the VSCode plugin.
From a Developers POV it's definitely easier to interact with a GUI.. and I '+1' on what u/rhacker said: the best UI in that case is probably the VSCode plugin.