Death to w3schools! When search engines allowed blacklisting domain, w3schools was my first and only pick. It always seems to show up on top for many web tech questions, but the quality is rubbish.

MDN is a breath of fresh air in this regard. I expect it will knock w3schools of it's search result throne in the coming years. The end of a era of low quality, ad sponsored (4 ads, just counted) web technology reference.

There are also lists for blacklisting github and stackoverflow content clone sites.