I've yet to do a hat top down so I'm interested in seeing what people have to say. I have one in mind that I'll start soon that will be a band joined at the ends and then the rest of the hat joined to it. I was thinking that there are at least two ways to do this that don't require seaming, one is to pick up and knit to the top of the hat, the other to knit the hat part, top down or bottom to top and then, using provision cast on(s) join with a 3 needle bind off.
You can't knit the left sock first. Ever.