When should one knead dough in a food processor vs. a stand mixer?
It's not preferable to use a food processor over a mixer with a hook, it's just a bit faster - food processors spin very rapidly and put a lot of energy into the dough quickly. A dough hook does the same thing, it just takes more time. A lot of it is personal preference, in my case I don't like either and prefer to knead by hand as I enjoy the process, if I am going to use a machine it's going to be my mixer with a hook as I can see the dough develop. With a food processor I'm constantly concerned it will self-destruct and take me with it in an explosion of polycarbonate shards, plus it turn dough rubbery very quickly if you leave it on too long.
So, use your hands, mixer or food processor, they will all get you there in the end.