Based on double optical pumping channels, we experimentally study the competition between two coexistent six-wave mixing (SWM) processes falling into two electromagnetically induced transparency windows by scanning the frequency of the probe field in two similar five-level atomic systems of 85Rb. By blocking one optical pumping channel unrelated to the four-wave mixing (FWM) process, one SWM process, together with the FWM process, generated by a conjugated small-angle static grating could be observed in the spectrum. Moreover, the other SWM process obtained by blocking the first SWM channel is also observed together with the FWM process in a lower N-type four-level subsystem. These experimental results agree well with theoretical predictions.