Well, all features come to Cider first, like I said, Calva uses Cider’s underlying backend and integrates it into VSCode.
More specifically, I’ll say Emacs better supports s-expression syntax and manipulation for it. And Cider has a better REPL integration. Calva faces limitations with what it can do in certain places due to the VSCode API, REPL being one of them.
Cider also has just more features, but it’ll be things like Cider inspector, or enlighten mode, or ability to macroexpand, etc. So less commonly relied on I’d say.
Cider has a better test runner too, Calva has some limits around running single tests and things like that.
Honestly, they differentiate mostly in the details, but I’d say try both, it won’t take long.