Hi David, here are some criteria for your choice:
– tablets are better if you need to move the person in a wheelchair for example, but the screen is smaller and it is more difficult to select cells in a smaller device
– laptop is a good compromise: it is both portable, can be used for someone lying in a bed (you need a bed table to support the laptop, such as the tables used for having lunch in the bed)
– desktop is a good solution if you already have a desktop; the advantage is the big screen, but you will need a rather big support to hold the screen if the person is lying in a bed.
Finally, it will also depend on the hardware you already own. Please remember that you will need a USB 3.0 to use Tobii EyeX or The Eye Tribe eye trackers; for tablets or laptops, it is a prerequisite, for desktops you can add USB 3.0 PCI cards (20 to 30€) if you don’t have USB 3.0 already.
Hope it helps
Pierre