disqus.com/. Drop in an iframe onto the page and you're done.

Disqus is a privacy violation.

replyable.com/2017/03/disqus-…
chrislema.com/killed-disqus-c…

Disqus also serves shady ads and is suuuuuper slow on the page

Google Plus. It's simpler to use than Disqus and it's backed by Google. Who knows, it might also give you some SEO advantage. I haven't personally used gPlus on any of my websites yet but I have been considering this for a long time, just too lazy to get it done. floaternet.com/gcomments

Thanks if i could pivot my question, What would your top 5 system for comments be? (the ones you would use?). Thank you in advance!