Most are all Free and all are rather fast, it's the speed our your internet service that determines your final speed
The problem is that youtube changes the rules to prevent, discourage or at least make it cumbersome for these download tools, so you have to update them from time to time.
Top 10 Best Free Youtube Downloaders from vloggergear.com
Free YouTube Download.
4K Video Downloader.
WinX YouTube Downloader.
Any Video Converter Free.
ISkySoft Video Downloader.
FastestTube.
Freemake Video Downloader.
ClipGrab.
All Video Downloader.
aTube Catcher.