It depends on what you want to do. Are you authenticating a human? Are you authenticating a machine? OAuth and simple API keys address very different concerns.

It depends on what you want to do. Are you authenticating a human? Are you authenticating a machine? OAuth and simple API keys address very different concerns. Generally Oauth is for authenticating to a 3rd party service/client that you are this account on this service. An API key is authenticating you via your client on this service. API keys are just like passwords. Only the user should know it, whereas OAuth tokens can be safely given to 3rd parties.