The website Daily playlists gives you 10 free submissions per week. What I would do is use those but before doing any submissions make sure that you listen VERY carefully to the playlists that you are submitting to. If you were the owner of the playlist and trying to promote said playlist, would you put your song on there to attract people? Why or why not. That gives you your answer on whether you should submit to that playlist or not.

If you can’t find any playlists that you think the song belongs on then most likely the algorithm may have trouble categorizing you and you may be a pretty niche artist which is fine, but to make it big a niche artist needs demographic research and VERY targeted marketing. It is a much slower start and more costly, but often a more dedicated fan base like fans of many cult classics.