Most of these are not open source and do not allow proper encrypted back ups. Google Authenticator in particular is awful from the regard. FreeOTP is no longer in development. Here are the apps you should be using:
Android - Aegis or AndOTP
iOS - Tofu or Authenticator

Cloud storage is frequently hacked, and should not be used for sensitive data or back ups. A better option is to use one of the apps I listed to make an encrypted back up locally.