To be fair, the only reason AV is terrible is because of all the awful mob movement patterns that result in needlessly larger pulls than intended, making it a nightmare for tanks and healers.
The vault is a healer nightmare cause people that ignore mechanics will drain your MP trying to fix their mistakes.
In SB, I'd say it would be Bardams that holds this honor as between the mobs hitting much harder, tedious 2nd boss and the healer pain of the last boss (granted not as difficult as the vault) it's just not very enjoyable overall.
