Greatest currently? I guess FFXIV.
It's a sad reflection on the state of the MMO genre if one of the candidates for current best game is a title that goes out of its way to be mediocre in almost every way possible.
The genre has matured.
A genre that was built to be a niche market for RPGers who wanted to advance to the next level has become a prepackaged nightmare of microtransactions, instant gratification, solitude and relative worthlessness.
What made you pick up an MMO was to be with losers like yourself willing to put in hours of work sculpting their online personas. A place where you could RP, a place where you could live out that DnD dream of fully immersing yourself in a character. Life be damned.
Many of us have aged out of that but that is essentially what an MMO did that other genres did not. Now that MMOs are just online, lobby-oriented RPGs in the way that CoD or fighting games do 'massively multiplayer' there is no real connection to anything.
The people you play with don't matter, the gear is constantly made obsolete and any attempts to roleplay is met with backlash from more mainstream gamers who see that stuff as unpalatable. MMORPGs have become junk food titles you play to pass time, with little consequence pumped out like McRibs with blustering marketing guys promising everything then serving up regurgitated ***.