In order to ease the pain of creating new accounts, many sites and apps allow users to use their social network credentials as a means of logging in. This saves the user from having to remember yet another login, and in return the service gets information from you social network. This seems fair since you would likely have to give them most of this info anyways if you were to sign up directly through them. But what info are these sights actually getting? And which of these social logins is actually supplying the most amount of info?
As you probably already expect, Facebook is the biggest culprit in supplying third party sites with tons of data. Because of all the data you give Facebook, they know everything about you including your name, address, current location, email, gender, friends, movies, music, and more. On top of that, by default, they even have access to all that same information from your your entire friends list. So if privacy in a major concern of yours, consider using social login other than Facebook.
Coming in a close second for the amount of data supplied to third party sites is LinkedIn. Since most people don't share as much information on LinkedIn as they do on Facebook, it is not as big of a deal. But this does not change the fact that LinkedIn is sharing all of your personal as well as your friends info with these third parties.
Google is next up on our list. Considering the amount of information that they actually know about you, they share a surprisingly small amount. In fact, the only information they share about you is your name, email, and address if given. They also are not opposed to sharing names and emails of friends as well. Compared to Facebook and LinkedIn, however, they do a pretty good job of keeping your info private.
When it comes to protecting your data Twitter proves to be king. Maybe its because they have the least amount of info, but whatever the case, when you sign up for a third party's service with twitter, you are only giving up your display name, profile photo, and the homepage linked to your profile. Given Twitter's open nature, they are all relatively easy to find anyway.
So in the end if privacy is your concern, be sure to use either you Google or Twitter login credentials. It really just comes down to what you want to protect more, your email or your Twitter handle.