Increasing DO is most effective with increased surface area of water to air. So the more contact between the water and the air the greater the exchange. Lots of smaller bubbles will achieve this, flooding and drianing in grow beds through a porus material, breaking the surface tension of the water, they all help.
I am not aware of any scientific studies as to which delivers the greatest results. The key is to have as much water surface coming in contact with air as possible to allow for the exchange to occur.
But now you have got me thinking... Time for another research binge.
