What social login would you most likely use on a new site?

If it was a public site for any user, I wouldn't offer just one because a single wrong choice could alienate the users you want to use the site. It's common to have a few such as Facebook, Google, Microsoft, and/or Twitter. If it was an enterprise site where the people in your company had to log in, I would use something as close to the technology stack I was using as possible. I'm thinking about something like Google or Microsoft, especially if you were using a specific workspace (email/docs/etc.) solution that was standard for the company.

If it's work related, Google. But I generally don't use any of my personal social accounts for logging in to anything.

I wouldn't. I never understood why localshop.com or thenews.com has to know my google account.

That kind of depends on what sort of service.

for me it might be twitter because it's almost like a throw away login for me.

or would you just use plain old email?

Metamask