I use 4KDownloader to download all the videos in the playlist from the YouTube. When there happens to be lot of videos in the playlist, there used to be a problem. The files take lot of time to parse and there is no option to download individual files on priority. So it is either all or none. When I looked for web based alternatives for this functionality, I came across this useful website - http://youtubemultidownloader.com/ which gives an option to download individual videos / playlist / Channels.
I have tried the individual videos and playlist options and both of them work fine. I used this site to download the videos of classic TV thriller - Rudhraveenai which was aired on Sun TV in early 2000's. The process is very simple:-
1. Copy the link of the indvidual video / playlist from YouTube
2. Go to http://youtubemultidownloader.com/ and click the appropriate button and paste the link.
3. Choose the desired resolution and file format.
4. Click the download link generated against the video thumbnail.
Hope you find this post useful.. :-)