Spotiflyer/Soundbound works great for me.

I personally use MetroPlayer and downlpad songs with spotiflyer. Spotiflyer just takes a link whether it be spotify or youtube and downloads it. You can put the link of your playlists or just individual songs. Some songs might give errors when downloading from spotify so if that happens use youtube as a backup. I have only had 6 songs fail so far with a playlist full of 700 songs.

Freetube, Individious, Piped, CloudTube, PokeTube, Tubo, Yattee are the main ones I know of. If you want be automatically redirected to alternative youtube frontends installed Lib Redirect.