Both seem fairly high quality to me, after reading the comments and viewing the pages from each site in comparison. I remember using w3schools to learn HTML pr

Both seem fairly high quality to me, after reading the comments and viewing the pages from each site in comparison. I remember using w3schools to learn HTML probably about twenty years ago now, and the content hasn't changed much since then. MDN appears to have gone through two major transitions within the past year. Whether those qualities are good or bad depend on your perspective; whether one of them ranks above the other in terms of SEO depends on the algorithms used by the search engine in question.