I've played quite a few MMO's over the years.
WoW, Aion, Tabula Rasa, Lineage 2, Guild Wars 2, Age of Conan, Warhammer Online, Final Fantasy XIV, Phantasy Star Online, Phantasy Star Online 2.
Most of the time I just lost the people I played with and once those games no longer have that element of "friends" they kinda get boring, and I can play most of them solo a lot ha ha.
The version of PSO2 that came over west is very late into the game and has had a lot of things ruined, the version I played was during the normal release and a fan translation of the JP version and on the JP servers.
FFXIV has the best story over all of all the ones I've played by far. There is a lot to do and you can do anything on one character which is nice, and is something that a lot of newer MMO's are now copying. The only things you will miss out on are the Timed events from Valentines, Christmas etc. But as the game is now so far along the experience in the older content has been change a lot and it no longer feels the same, it is sadly not the same experience as playing each expansion at release.
As for games like Warframe and Monster Hunter, I find these more fun now as they are more pick up and play, no real requirements to always be playing, which I like.
I've started playing Warframe again just the other day and caught up on the main story, the game actually has a good story to it as well.