I would recommend either Aegis or andOTP. They are basically the same, open source and all, but I do agree that Aegis ends ups having a better looking UI. andOTP is more "basic" but features a lot more of customization, so I guess it's more geared towards the advanced users.
The benefit of both of these apps is that you can keep encrypted backups of your keys. So even if you loose your phone, provided you have those backups, you can simply import them into a new installation of andOTP or Aegis and the programs will automatically implement your keys without the need to have them in a random piece of file/paper.