I nominate GBFL Confederations Cup, all of the staff dedicated a lot of their time (like every year) to organize this event.
I also expected at least one of the servers I hosted this year to be in this, I know this is only the 3rd page of posts of this topic (thank you WALDO for your nomination) but I try to host different servers (other than jailbreak, city rp...) every months or so, and they seemed to be popular everytime they were hosted (atleast during the few weeks after opening)
It's been a few years since I host LEGO Block Party, Blockland Cinema, Staircase to Heaven, Christmas Giftbuild and GBFL events with all the team, but I start to wonder if it's really worth the work on these anymore... :l