Ferric Chloride or Muriatic Acid + Hydrogen Peroxide for etching?
I've switched from FeCl to acid/hydrogen peroxide exclusively, in my experience it has an extremely short shelf life but considering how cheap it is that hardly matters, the main benefits are etching speed and results, FeCl takes 3 to 4 times longer than a new batch of acid/hydrogen peroxide and with the latter I've done tracks down to 0.2mm with no problems.