Downloading YouTube Videos in a Playlist

Again, JDownloader 2 is the tool for you. With JDownloader 2 running, just copy the URL of the YouTube playlist. JDownloader will pick it up and start processing the whole playlist.
With each video in the playlist, by default, you'll get a video file, an audio file, an image file, and some text files - typically subtitles and file descriptions. With the video and audio file, you get multiple variants, if supported by YouTube - different filetypes, resolutions, fps, video/audio codecs, and bitrates.

To remove certain filetypes from the download queue, go to the Linkgrabber tab and enable Filetypes on the right panel. From there, de-select the filetypes you don't want to download.
If you have only a few files, simply select the audio/video variants you want from the drop-down lists beside the remaining files in the main window. If the playlist is composed of hundreds of files, we need a better solution. Again, on the right panel, enable Hoster. Right-click on youtube.com, and select the "Change variant" option.