I had my first mother in the same E&F system as my other plants and once it started getting big, it quickly overgrew the other plants. I think people suggest growing mothers in soil because plants don't grow as fast in soil. I ended up taking two generations of cuttings from her and then flowering her because she was so massive. It really just depends on how much room you can afford to give her. Obviously you will be able to take more cuttings from a plant that grows faster, but for convenience and space I'd say put her in soil.