In a nutshell: doesn't worth - details below.
I'm from retail, 14 days left on my acc, but I'm leaving it there coz how I'm disgusted from retail (don't even know why I gave it another chance after I almost vomitted 4 moths ago, owell...) current content (Legion) sucks, imho - I'm aware how blizzard is addicted to all of this fel magic / green demon sh*t, but what is going on retail is hilarious, we get it blizzard, you love green, you love demons.. let's just get over with it, and try something else, because 98.7% of your playerbase is dying of boredom from "LEGION, LEGION LEGIOOOOON OMGWTF". They just can't stop this, I started to think of they are under the control of Sargeras itself, after all these years... The daily grindfest disgusts me, just the thought of it... you have to quest to open dungeons (yea you read it right), you have to grind through RNG lootboxes to get legendary items(dropchance = 0.00001% kind of), to actually worth something in the game, likeee wtf?!... item level literally 1000 (no kidding, legendaries are going this itemlvls nowadays), for what reason?? They could just squish the ilvl back to 277 (just a thought, nvm). So retail is now like, more focusing of wasting players' time by all of this grindfest, rather then the content, just to ensure themselves that the company gets its money (because we are wasting time on farming), from us.. players.. To be honest: WoTLK or TBC were actually THE expacs. After that, the game totally lost its point: fun. I can't go raid there, because I have to grind the legendaries, or the worldquest for the artifact power... If I go raid, what I get from bosses is gold (worthless, nuff said), or a random 1hour buff called augmentation... items drop at exclusively low rate, which would be ok, if a raid wouldnt last a forever time (even without wipes)... even here in wotlk the drop rates were "low", buuut the fun was fking high. so in sum: retail = timeconsuming grindfest, without any fun. private server with wotlk or tbc content = fun, not that time consuming, not based on grinding!!!! So I vote private servers over retail. My last hope on retail is for the next expac, called Battle for Azeroth, where the game actually will feel like in vanilla (horde vs alliance, random themed raids (AND NOT LEGION ONLY FOCUSED duhhhhh...))
currently i'm seeing legion even in my dreams, all i see is green.. thx to retail xD