I haven't watched clannad (Ikr!!! WTF is wrong with me!!!!) It will probably be that one....... But right now I would say ANOHANA!!!!!
That was sad as fuck!!!!!! Definitely one of the best 12 episode animes!!!!!
I also haven't watch Sakurasou, Suzumiya and Chunibyou from that list.
But Kokoro Connect and Torodora was also VERY GOOD!!!!!
Pocky Lover Boy!