Adding blocklists is a personal choice. I run the default lists and am satisfied with them. If you add some, ensure they are properly formatted for Pi-Hole (hosts format).
The lists from waLLy3k are known to be compatible with Pi-Hole.
Edit - note that adding more blocklists will result in more false positives, which can cause annoyance and frustration on the part of your network users. You may want to locally block undesired domains with either blacklist or wiildcard/regex entries. This puts you in control of what is blocked and you are not at the mercy of a list maintainer.