learn your class

I also Really like Summonstone. It doesn't have guides for every spec yet but what it has is simple too the point and edited by very high level raiders.
summonstone.com/

Edit: Also Here is the current 6.2 patch dps rankings. i.imgur.com/KEyF7WR.png Now obviously these are not perfect but they give you somewhat of an idea of what is strongest right now. There will also likely be hotfixes before mythic week so don't give up hope if there is a spec you particularly enjoy. Unless its demonology. They hate demonology and they want it dead and gone.

Here is also thoughts about all dps classes and specs written down by a mythic raider from midwinter one of the top guilds in the world. docs.google.com/document/d/1ZjS3wYgrfubyoCH_mB08aW7UElVCrDlxHxz8OXE6gT0/preview?sle=true

This was based off the ptr changes of a few days ago however so some of the points may be off due to trinket nerfs or the like.