I was in your shoes about 5 weeks ago.  I started on classic it's slow leveling and a lot of quests without a true storyline.  Then tried Cataclysm and leveling was slightly faster but still didn't like the game I was playing.  Then before quitting I tried retail.  I got drawn in initially by the dragonflight questing and story.  Hit level 70.  I have to say that the war within story is excellent so far.  I do feel like I have jumped in to a book towards the end but I don't feel like I'm lost though.  I was worried that retails rotations would be too much but I'm pleasantly surprised.  Now after a month I'm not ready for mythic runs but I do understand my abilities and the order to use them.  I'm looking forward to playing like I used to during my 20's and get that similar dopamine hit that I used to.  I don't understand everything.  I plan on using a feature to level alts through each expansion in the future so I can know the whole story eventually.

TLDR 
Try the different versions of the game find your niche.  Just do it don't be intimidated by 20 years of content.