For our 2FA security process, if you already have an authenticator app, by all means, use the one you already have*, but if you don’t yet have an authenticator app, our primary recommendation is to use
Google Authenticator. Google Authenticator is a best-in-class provider of two-factor identification. It is easy to use and quite versatile.
We had previously recommended using Authy, however, and while a perfectly suitable 2FA application, its user interface is not as intuitive as Google Authenticator's interface.
*Except Duo, please do not use Duo. It is not calibrated correctly with our 2FA.