I like reddits system. Pick a user and pass. All other fields are optional, and you can fill them out later if you wish or as needed.<p>Imo if your website doesn't use that system its because you're more interested in collecting and selling my private information than you are providing me with whatever service you want me to sign up for.
These arguments are not arguments in favour of social login, they are arguments in favour of <i>third party authentication</i>.<p>OAuth as an authentication method is stupid. Use Persona (<a href="https://www.mozilla.org/en-US/persona/" rel="nofollow">https://www.mozilla.org/en-US/persona/</a>). Third party auth done right.