We have entertainment website. Users geo is 50% USA/Canada, 30% Europe, 10% Asia, 10% Other.
How do you think which signup form will work best? Regular signup / OpenId / FacebookConnect+Twitter? Maybe you have some statistics? Or maybe I should do all of them? :)
As Facebook has many, many groups about Games, I suggest you start with Facebook and add the one or the other Solution with the time.
If you have a Group at Facebook, why not publish the new Login-Methode there or start a discussion what your Users are more likely to have.
I would do all of them, or some subset of those. It seems like a lot of websites these days give users more than one way of registering. You want to remove as many barriers as possible for your users. Choosing to register on a website is actually a big deal.