E-mail or Moble Authentication?
Authenticator, especially if it is on a different physical device than the computer where you play the game.
There is a restoration service. See: https://en.support.guildwars2.com/app/answers/detail/a_id/9274 for details and strings attached.
I have email authentication turned on but so far I haven’t needed it – I’ve never had a login attempt that wasn’t me. Admittedly I don’t know if they’ve even tried, but if they have then a unique password has been enough.
“Life’s a journey, not a destination.”
authenticator will always be more secure simply due to the fact that it generates a random number somewhat often (talking about every 30second or something, not sure on the exact time though) you need to type in to get access, where an email they “just” have to find out your password to your mail as well as your game account to login