Which App Engine Authentication Method should I choose? (Pros/Cons)

Question

I am experimenting with Google App Engine and as I went to create an app it asked me to choose an authentication method. Options are 'Google Account' or 'OpenID', the 'Google Apps Domain' option doesn't interest me. However, I can't find very much information in the documentation that lists pros/cons of either method.

My question is what are the pros and cons of each of the methods?

Thanks.