P-Channel devices are usually more expensive and have other design considerations, so I design 99% of the time with N-channel and have several devices rolling around my parts bin when I need one. It's 6 of one, a half dozen of the other. You might be able to save a little power by using one or the other, since a comms channel is usually idle a lot - I have not had a design where I needed to care about power and also needed a cheap comms interface, so I really have not thought it through.