I think of it as maybe try mouth, foot or head mouse first, then if/when those don't work, some kind of twitch switch, then eye gaze if/as progression dictates. But that really depends on what is most comfortable/possible for a given person.
And of course voice recognition as long as there is voice. If you can be more specific about the abilities of the PALS and the devices/computing platform s/he seeks to access, we can prob be more helpful.