Well I think that lots of people have killed heroic bosses in this tier. It is widely known that Sha HC is the hardest of this tier, but what about the other bosses? Which you think to be the second hardest one bestides Sha?
As for me I would vote on Shek'zeer at the moment ( I havent tried Tsulong, lot of people say that he is really tough) not because of the difficulity but rather the insane burst, which she makes in P1: if your healers don't know how to do everything perfectly ( 4 healer fight, gonna love it) then it is a wipefest.
So who is the hardest according to your opinion?