I know some MMOs technically don't have a typical "endgame" like WoW does. For example EVE the entire game is sorta end game. Hence the quotes around "endgame". But I mean doing the stuff considered late game stuff. Like in EVE, typically you wouldn't (without outside help anyway) as a 100% new completely fresh player without skilling up or anything take part in the huge pvp wars that happen or have the funds (or skills) to do moon mining or even have funds for titans or the player stations and what not.
For me...I probably lasted longest in EVE. Even though I played WoW for longer. In EVE, I stayed in nullsec as soon as I could, I sniped any players that came by (nullsec at the time I played was safer than highsec, and almost always empty where I was, probably different now) and was pretty much a pirate. Then I got recruited to a pirate group that noticed me and for 15 months I did what I considered the endgame stuff with them. They already had a station of themselves and a titan when I joined, but I left about the time they lost both of them in a large war and they picked the wrong side to be a mercenary with. Felt like I pretty much did the most amazing things I ever did an MMO and wanted to leave on a good note before getting worn out with the game.
But even though my group I was in lost (we were really pretty much mercenaries not really allied with anyone), that war had to be the best most amazing thing I ever was a part of in an MMO.
WoW on other hand...well...despite how long I stayed with it through so many expansions...I probably actually lasted the longest in legion at endgame. The other expansions I got pretty bored with reaching endgame and either made alts or quit. Legion I lasted 9 months at endgame and that was my favorite expansion and then I made a bunch of alts, leveled them up, did another 4 months at endgame to unlock some allied races and quit in BFA. Close up of Legion, I stayed 7 months at endgame for WoD so that was quite a bit. Didn't bother leveling alts though.
Those two probably be most I stuck with at endgame.
Keep in mind, that isn't my entire time I played. Just how many hours I stuck with at the "end".
My Skyrim, Fallout 4, Starbound and WoW + other game mods at MODDB: