I think it depends on who you want to use it. For example, I installed Facebook comments on my company website solely so people could leave comments using a service they were probably already logged into. For a coding blog I would never use Facebook, but I would look around for a service that used Github Oauth. Basically, I think if someone needs to sign up to leave a comment, you will never get any comments.
For my own blog, I don't bother with comments. I just cross-post here. 😉
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