IMHO this mostly depends on personal priorotiespriorities, whether you/ the user prefers to use your username or your email address to login to a website.
For a project I just implemented the option to use either your usenameusername oror your email address to login – and I suppose that nowadays actually many websites allow to use either or.
[edit] Some additional thought: I just checked xing.com and linkedin.com and plus.google.com and ello.co and pinterest.com – but they all ask for the email address. At least they suggest to use the email address – maybe it would also be possible to login entering the username. So maybe it actually is a bit more user friendly for both user and site admin in case somebody forgets his/her password.
In this quick round-look I could only find twitter.com offering login through email address or username or phone number.