Oooh.... Hmm... You're right, it is difficult. My favorite right now is probably the rare pair bang. It's very exciting to see so many people get excited about their tiny ships and have a place to hype them up. My least favorite event, I didn't even get to properly kick off. I tried to do an "award ceremony" last year that was just people gifting themselves, their friends, and favorite writers by dropping names and recs that fit different themes. But since a bunch of people didn't read any of the info for it and ignored the IC that asked for suggestions on what the categories would be, it got blown out of proportion and they thought it was being exclusionary to only the popular people in fandom. When really it was meant to be: "favorite angst fic?" "Oh! I love this fic by X, or I wrote this angst fic I really love!"