The best Youtube downloading facilities often come as extensions to specific browsers. Since you've not told us which browser you're using, it's therefore difficult to point you in the right direction.
I use Firefox, with this extension installed:
https://addons.mozilla.org/en-GB/firefox/addon/easy-youtube-video-download/
The guy behind it is always on the ball whenever Google changes the coding used on Youtube pages (which renders most downloading programs and extensions inoperable), so that any problems are quickly fixed. The extension is free but some functions only work if you've made a small donation to the developer's 'coffee fund'. You can choose any amount you like or, if you're a skinflint and don't want to pay anything, you can simply click on this link:
https://videodroid.org/thanks_for_support.html
(That places a cookie on your browser, which tells the extension that you've made a donation, even though you haven't).
[If you install that extension into Firefox, and see a message about a fix to it still awaiting approval from Mozilla, don't worry. The developer forgot to remove that message after everything was sorted out; the extension will still work].
Remember though that it's illegal to save Youtube videos, which is why Google keeps changing the coding on Youtube pages (in an effort to thwart downloading software). So you shouldn't be surprised when
any method of saving Youtube videos ceases working for a while.