[somepig]

regular "app based" is just OATH-TOTP in most cases. This uses a shared secret and the time to generate one time codes.

The Yubikey explicitly supports TOTP, and will happily store your secret on the key. You can then use Yubioath to pull codes from the Yubikey as needed.

I'm a huge fan of the ability to use either U2F or TOTP with the same hardware token.

[mfontani]

Note that the Yubikey only supports up to 32 TOTP.