I think a username works better here. Gives users more of an ability to customise their profile than an email would, might be a tiny bit more secure than with a

I think a username works better here. Gives users more of an ability to customise their profile than an email would, might be a tiny bit more secure than with an email address (since someone with a hacked list of emails and passwords can't just test them out on the login form) and generally I feel it looks better to have a human readable username than a generic email address to log in with. More importantly however is giving the user a way to choose what name is displayed in their profile/next to their content, and not doing stupid things like forcing a name based on the email address or trying to take the first and last names from a connected social media account.