Just started playing. A friend used Maarek Stele and his text reads "When your attack deals a faceup Damage card to the defender, instead draw 3 Damage cards, chose 1 to deal, and discard the others."

So does the attacker pick the card or the defender? I thought defender he though attacker so now I am wondering.

I believe the attacker (player fielding Marek Steele) would pick the card. This essentially allows you to pick (from a hand of three) which critical hit will effect your opponent.

Although the wording of the card is a bit ambiguous, I think the intent is that the defender draws three cards and the attacker gets to pick the one that is applied, as Spyral said. Certainly there should be no mixing of the damage decks, as a literal reading could lead to.

Yup yup. I think that works