Cataclysm (Dec. 2010-Sept. 2012)
Mists of Pandaria (Sept. 2012-Nov. 2014)
Warlords of Draenor (Nov. 2014-Aug. 2016)
Legion (Aug. 2016-Aug. 2018)
Battle for Azeroth (Aug. 2018 - *Dec. 2020)
* - ON OR BEFORE DECEMBER 2020.
Which one was the best?
Anyways the GOAT expansion is Legion hands down followed tail gating close by Mists of Pandaria, GOAT. SR, as I call it.
For those uneducated about what a decade means:
https://en.m.wikipedia.org/wiki/2010s