My guild currenty have MSV down (ofc -.-'), and 3/6 in HoF (getting Wind Lord down before next reset)
I hear Protectors are pretty easy if you do the Koalon --> Regail --> Asani, but is it easier than Ambershaper + Shek'zeer?
Well if you want an honest answer, they're all easy in normal mode (except Empress and Sha sort of). There's no reason not to just go 5/6 HOF then 3/4 Terrace.
Have to complete HoF in order to do Terrace. Everything in Terrace is easier than the final two bosses in HoF, Sha being more difficult than the other 3 in Terrace, but I'd say a little easier than either Amber or Empress.