It all depends on what you want to do with it. If you do much typing a laptop is much better. If your going to use it mainly a home, get a laptop.
I don't find tablets very comfortable to use. I either have to bend over it while it's perched on my knee or table; or hold it like a book. With a laptop I can angle the screen to suit me.
A laptop is more powerful (usually), is upgradeable but heavier.
Personally, assuming that you have limited head movement, I would have thought a completely separate screen and keyboard would allow you to arrange them into relative positions that provide the minimum discomfort.