Scarlet Monastery took like 7 attempts for me and shado pan monastery was a 1 shot.
Everything else was between 2-5 attempts. Siege was about 5 so I would rate it from hardest to easiest
1. Scarlet Monastery
2. Siege of Niuzao temple
3. Mogu'Shan Palace
4. Stormstout Brewery
5. Scholomance
6. Temple of the Jade serpent
7. Gate
8. Scarlet Halls.
9. Shado Pan Monastery