I'd recommend Cairne over the 2 others though (unless you want a lategame finisher).
Don't craft Ysera first, she only fits pure control decks, but to play control decks you will need much more legendaries. People who recommend her have no idea how useless she can be since she makes you "skip" a turn.
Once you have your core legendaries (basically the 3 I mentionned early, + sylvanas maybe), get the versatile ones, Tinkmaster then Thalnos or Nat depending on your needs (Nat for Priest, Thalnos is quite useless in priest decks).
Oh and get a faceless manipulator, it's kind of a 400 dust legendary.