Mine would have to be the Easter event, specifically the N.E.W.S. event. Man... that thing was legendary. It was a great break every hour from grinding and guaranteed like 15-20% (I was 2nd/3rd job at the time so idk about 4th job).
I may not have went through all the events but xmas/winter is my fav thus far. I love the design in fm and henesys, also the sound track couples well. Great work by the dev team.
Xmas, love the Gelts and retrying to Chaos a nose without success year after year. Could be Halloween if we got 1 perma purple belt with 1 slot each year but y'know for some reason we place dumb ass dojo on this pedestal despite that not being gms like in the slightest fucking fuck