Now and then I need/want to download a YouTube video, especially when I've used the YouTube Editor to crop/combine videos.
The best tool I've found is ClipConverter.cc.
Go to ClipConverter.cc and enter the viewing URL for the YouTube video. Click on "Continue".
On the next screen, chose what resolution you want and click on "Start".
When the conversion has completed, click on "Download".
Realize that downloading from YouTube is just a little bit shady. Beware of unwanted pop-ups/-unders.