If you are the only user for your headset, then the Iris Scan will be the most convenient method to manage the device. A benefit of this system is that it will load the results of the calibration app when you log in. More info at Manage user identity and login for HoloLens | Microsoft Docs
However if you are going to have multiple people using the device (such as a classroom setting) then you want a streamlined way for users to be able to quickly use the device.
We recommend that you set up a single account for the device, and then remove the need to sign in on the device when turning the headset on.
To do this, launch the Settings menu, select Accounts, then the Sign-in options tab on the left hand side, and change the Require sign-in option to Never.
Then simply exit out of the settings menu. Now when the headset is launched it will allow you to operate without any sign in. (Note, after some OS updates it may require you to put in your PIN to start the device, so you should also have the PIN number written down and stored in the case with the device).