I prefer larger floaters such as water lettuce and frogbit that are easy to contain inside barrier which I constructed from airline hose and tied the barrier ring to a piece of sinking anchor with a fishline. Their roots are long and serve as breeder mops for fry and surface dwellers to hide. I will stay away from small floaters such as Duckweed, Azolla and Salvinia which can multiply and escape out of control, and hard to get rid of if one decides not to keep. Besides they have short roots not of much use for hiding.