Echo Echo is very user friendly, although, it doesn't contain a lot of information other websites do contain. Other than that, it is quite helpful.
W3bschools is very descriptive in their work, although its all clumped together and extremely hard to find one single thing. I would still recommend this to anyone trying to learn HTML.
HTML.com is what I would prefer if I'm having problems with HTML coding, it's clean, quick, and you don't have to search through a whole bunch of stuff just to find what you're looking for. Although on the other hand, it's very simplistic, and may not give you all you need. I recommend this site to a certain extent.