Code is not based on atom, it's based on Electron, which is the runtime (node+webkit without the UI chrome).

VSCode has lower typing latency and a more considered system for building / debugging / code completion. Atom has a richer plugin api and has been around longer so it has more plugins. I've done basic plugins for both and plan on using/developing for VSCode but I've been too lazy to write Vim bindings and not willing to use the editor without them.