The TLDR is that, among the Firefox forks, Waterfox is pretty bland, which can be both good or bad depending on how you look at it. It’s not as private as LibreWolf or Mullvad Browser, it doesn’t have a unique aesthetic like Zen Browser, and it is not as customisable as Floorp. But all of those addition bits can come with some tradeoffs.

In my opinion, Firefox is suitable for most people, LibreWolf for additional privacy, Zen if you like the look, and Floorp for extra customisability OOTB. Waterfox is really only if you don’t need those additional bits, you dislike Mozilla, and you don’t want a Chromium browser.

Note that Waterfox was purchased by System1, an advertising company at one point, then ties were cut off recently. The fact that they could be acquired by an unfriendly corporation could be a concern for you, and might push you towards more community-oriented options like LibreWolf.