There seems to be almost as much content in the two new expansions as the base game. So I reckon they might be pricey. Theoretically, if I was only going to buy one, would 1st edition players recommend Recurring Nightmares or Suppressed Memories?
It's purely a matter of taste and largely depends on which investigators you want. None of the Arkham files minis are anything special.
I would get Recurring Nightmares because of Shoggoths and Mi-go.