It's really hard picking one! But I think I'm going to go with 2011, because the h-staff pulled a fast one and swapped around our forums! Along with the awesome word swaps. 2012 was pretty fun to post as Lerroux though.
Uh this year I think I am good with anything, as long as there's something. *shrugs*
I got to witness Applesauce Day and Lerroux in my old accounts, but I never really touched my account in the Lerroux one and I only opened it to check what the prank was lol. I wish I was around during the Everyone-Is-A-Mod prank, it would have been fun. My favourite so far is Applesauce Day. <3 Especially reading the one bio saying "I love roleplaying", into "I love buffalos" I laughed so hard omg. Ok I'll shut up now.
I don't know of any suggestions for a prank, but I hope they have one. If they don't it would be disappointing. :(