I have used both Crowns and Membership before (I have purchased up to Caliburn) and I would strongly recommend that you instead get a membership. You then can go to all of those places! If you are stuck on using crowns. I would say probably Mount Olympus because it is a repeatable dungeon and you can get some pretty good loot. 2nd Choice would be whatever you need for the Main Storyline (so Iron Works?) That is just my suggestion! Good luck!