I do not have info about the Royal Games Castle or Blossom Dojo.
I would recommend the Fey Courthouse over the Celtic Castle.
The Courthouse only drops 1,000 coins at a time where the Castle drops 1,400 at a time. However, you can collect every 4 hours so you get more coins in the same period of time. Plus, the Courthouse has a chance to drop Golden Nuggets and other items. The Castle only drops coins.