With Irresistible Faefolk, who is the attacker?

You are the attacker — you applied "Contested" to the battlefield first when you moved Faefolk there, so you keep the Attacker designation even though your ability pulled the enemy unit in (Rule 459.2.b.1).

Exception: if you move Faefolk into a battlefield your opponent already contested, they remain the attacker and you're the defender.