Best Guides to learn content

[Enla]

I wouldn't recommend Mr Happy at all. I still remember the days when Weeping City was new and his outright misinformed guide on Ozma led to MANY a raid wipe, often to the point where I made a specific post before that boss on every run with the correct strat because lo and behold, most people only did it his way.

[MeganLynn]

Graehl Gaming is hands down the best at explaining everything you need to know about an encounter, be it trials, dungeons or what have you! And the videos are made extremely well!

[Lodinn]

MTQ is half-speculative as well because she makes guides for the content before killing it herself so there are plain errors in her early guides. Later on, it boils down to personal preference.
Current tier text guides can be found at http://clees.me/guides/, they're quite ok.
https://www.mooglemedia.com/category/class-guides/ - neat hub made by a bunch of good players who write class guides including itemization.