Both.. The mind is willing ( to stand) but the back has the final say. Unfortunately the ol' back ain't what it used to be so I'll start out standing, taking a seat when I have longer, more or less "straighter" cuts, then stand again when I need to make more accurate cuts.. Weird I know but for some reason, I seem to have more control while standing..
Eventually, I would like to get a foot switch (probably not until I get my next saw) and when I do, I'll most likely do more sitting than standing..