If your client can speak, RTI has just announced a voice control driver.[Link: rticorp.com]
If the client cannot speak, and can use touch pads with the mouth stick, I think that a pad based system would be the easiest to use. URC, RTI, and others offer pad based control. I recommend sticking with systems that allow customizing the screen layout and button response because you may need to accommodate touch quirks. In your programming, you'll want to minimize the number of presses -- "one touch" should be the rule. Another plus is the ability to update the program wirelessly because the "remote" may be lashed in place and hard to extract in order to make a connection. Ideally, a cloud based update would be great as this would save you a trip to the site as updates are applied and tested.
Another point to consider is how the IR reaches components. If the remote is lashed to a bed or chair, it might not be pointing in a good direction. WiFi and RF based remotes will not have this issue. Otherwise you may need to include some sort of IR repeater.