It is difficult to say which method is better, it depends on other factors like Hz. You can see https://books.google.com.tr/books?id=ZURZDwAAQBAJ&pg=PA248&lpg=PA248&dq=electrostatic+pesticide+application+unipolar+or+bipolar&source=bl&ots=uwTN8cz-b1&sig=ACfU3U3ov6j81ueJTRuYZIWnxvMXzeIizg&hl=ar&sa=X&ved=2ahUKEwi4nZSBtInkAhVwwqYKHU8eB44Q6AEwEnoECAkQAQ#v=onepage&q=electrostatic%20pesticide%20application%20unipolar%20or%20bipolar&f=false
It depends on what kind of atomization principle nozzle you have and what is the spray pattern.
please refer to the article
Law, S.E. 1978. Embedded-electrode electrostatic-induction spray-charging nozzle: theoretical and engineering design [in the overall process of electrostatic deposition of liquid pesticide droplets onto agricultural plants.
In my view bipolar charging is more suitable for non-conductive and electrically isolated charges.