Today’s app is Authenticator Plus It’s available for both Android and iOS and will save you a lot of hassle if your phone dies on you like mine did. On an unrelated note, I do not recommend the Nexus 5x but you can’t buy new ones anyway so that’s kind of a wash.
Authenticator Plus, on the other hand, is great! It stores your accounts in your dropbox so you can simply sync them onto another device if you can’t use your usual device (don’t forget to factory reset it if you lost it!) instead of going through the slow and tedious process of using recovery codes to get back into your accounts. Don’t worry, you have to set a master password to access your accounts on a new device.
Full disclosure: Authy does the same thing and is free where Authenticator Plus is paid. One of my coworkers likes it and another one didn’t like the onboarding process, so you’re going to have to make your own decision there :) I started with Authenticator Plus and can’t be bothered to switch everything to Authy just to try it out so I’ll be no help there.
And while I’m at it, don’t use SMS for your two factor auth! Sure, odds are against anyone bothering to attack you personally but why take the risk?