I disagree with Control Blood and Elana Seraph being the answers.
I play Control Blood, Aggro Blood, Elana Seraph, and Tempo Rune.
Tempo Rune: Aggro Blood, Tempo Rune, and to an extent, Combo/Tempo Forest Decks seems to give it most trouble. There was one shadowdeck I faced that felt like it countered Tempo Rune well but I never saw it again.
Tempo Rune eats up Control Blood and Elana Seraph.
Aggro Blood: Trouble against Elana Seraph, against other Aggro blood it becomes who draws better, Midrange Sword can be trouble some if they play smart, and Combo Forest decks. But I haven't played Combo Forest personally so I don't know if they have to draw well for that.
If you're trying to counter them both, I'd go for Tempo Rune, Combo Forest, or Aggro Blood.
Be the monster to beat the monsters : p