the user who submits the video has the original. they upload the original to youtube and a bit of quality is lost from the conversion. if you optimize settings before upload, you still lose a little bit of quality but not too noticeable. i think thats common knowledge right.
but when you download from youtube, using whatever downloader is the best, and saves it to flv mp4 or whatever is the highest you can get… will you lose a bit of quality from what you are seeing on youtube? ie. are directing downloading the video from the source code of that videos page? is any quality lost at all when you download the video from youtube basically