What's better?
Login Button
OAuth Dialog
I like the Login Button because it shows profile pictures of the user's friends who have already signed up for your application and it opens a dialog overlay instead redirecting to a new page as does the OAuth Dialog.
But, I think the OAuth Dialog is newer. Which should we use?
Also, the Login Button is XFBML. Apparently, Facebook is in the process of deprecating FBML. Does that mean XFBML is being deprecated too?
It isn't that one is better than the other - they are intended to accomplish different things.
The login button is used for external websites to allow Facebook-based social elements and community within that site. You can then add other plugins such as comments, the like button or the face pile to further integrate the Facebook social networking aspects, with the login button acting as the authentication mechanism.
The OAuth dialog is specifically for FB apps that run within the Facebook canvas, and allows you to request Graph API permissions from a user which will grant you access to various parts of their profile and additional channels of communication.
While Facebook is deprecating FBML, they are not including XFBML elements that support social plugins, such as the login button. See here for more info.
I think Daniel hit the nail on the head.
I have just started reading up on Facebook Development, and it seems they are providing a great set of tools to do very powerful things, but they aren't particularly explaining which bits do what.
I think you need to be sure of the difference between; a) creating a web app that will leverage the facebook api to enhance its functionality (i.e. using the login button to allow a user to login/create a profile on that website) and b) creating a Facebook app that makes use of the api to simplify development (i.e. authorize and authenticate a facebook user for an app request)
I don't think they have outlined that distinction very well throughout their documentation
The oAuth button is decidedly and absolutely better for a simple reason - it is documented and relatively stable.
The Login Button has nearly no documentation right now ( https://developers.facebook.com/docs/reference/plugins/login/ ), and the behavior has slightly changed several times.
The documentation for the login button is currently limited to how you can :
For the last several months ( ~Jan - July 2012 ), the documentation has not included anything concerning the flow of information or status -- ie, what actually happens on a successful or failed login.
While there are answers to these questions on StackOverflow , and mentions of other parameters that seem to work when passed in, Facebook does not mention or document any of this functionality at all, so it is essentially use at your own risk. The LoginButton is essentially a black box of mystery, that people just seem to have working thanks to undocumented features, and with functionality that will change/cease on random weekly updates.
tl;dr - stay the f(*& away from the Login Button and just use oAuth
