In a n-channel JEFT, the channel is n-type, and gate is p-type that means the majority carriers across the channel are electrons. the opposite is for p-channel JFET where majority carriers are holes. Accordingly the polarities of the voltage supplies change while biasing them. To switch off an n-channel device requires a negative gate-source voltage (VGS). Conversely, to switch off a p-channel device requires positive VGS.
Also n-channel JFET are faster than p-channel, because of higher packing density, and electron move faster than holes, in other words, electron have higher mobility than holes.