Is it better to use Royal icing or Buttercream for the Brushed Embroidery look with piped flowers? I practised a bit on parchment paper and after it hardened the Royal icing broke very easily and I'm worried it might crumble off my cake after it dries. (I don't use Royal icing very often)
I would suggest using Royal Icing directly onto the cake.
Definitely royal. The reason it crumbled is because you put it on a moveable piece of paper. When it's on the cake it will stay put because the surface is "fixed".