Past work, it would have been Identity Finder by a landslide. Awful UI, awful support, super intrusive, a total pain to administer, just bleh. Glad I was able to wash my hands of that.
Personal stuff, iTunes. I genuinely like the interface (at least on macOS) but it's huge and bloated and doesn't do some of the things I want it to. If they ripped out everything that wasn't related to listening to your personal (local) music library, I'd probably like it quite a bit. I wish it would write metadata to file tags rather than its own database, but I forgo that if it got rid of all the other crap.