The most convenient, reliable, and easy to use video downloader for Youtube right now (and for a long time, the creator is very good about maintaining this product, which requires constant battling with YouTube's countermeasures). It is absolutely worth donating to get the PRO features. For myself specifically, I mostly use the direct to .mp3 option which pulls the highest quality bitrate available in my desired format, in one quick step straight from the video page. Very powerful, has let me continue to supplement my personal offline music collection via Youtube with ease.
Undoubtedly also excellent for videos where you want to pull video files too.