I always leave the fish alive as much as possible until I am ready to leave for two reasons, the later being I believe the fish is fresher than sitting dead all day on the bank or water in the sun etc; I rarely cut the gills I just reach inside the gill plate and hook my index finger in the notch of the outer gill and give a quick jerk which severs a major artery. A bit morbid but if you get it at the right spot it will shoot out with every heart beat. I then let the fish bleed itself for several minutes until I no longer see a steady stream of blood. I then gut and remove the blood line from the spine prior to packing them out.