Best ways to download YouTube videos

We teachers need to download videos from internet often. I have tried many softwares to download these videos but usually these free to use software programs don't give you the satisfactory results. I searched online to find best ways to download 'YouTube' videos and sharing the result of my findings.

YouTube is the most popular video sharing site on the internet, allows its users to upload and share videos easily but doesn’t provide any way to download them.

Best ways to download YouTube videos:
I don't recommend using professional downloading software programs to download YouTube videos, as there are many ways to grab these videos and save at your pc hard disk.