Contrary to what others have said here, I haven't actually experienced much better speed in Mavericks than High Sierra or even Mojave (I'm on a 2010 MacBook). Snow Leopard and Lion definitely boot and run noticeably faster, but OS X was already getting pretty heavy by Mountain Lion/Mavericks. Unless your machine doesn't support the latest OS or you need to run old software, I really don't see much reason to stick with an old version.
For all that's said about 10.6 being the pinnacle of OS X, I disagree. After using more modern versions, it feels very dated -- it lacks notifications, full screen/spaces, and the super intuitive and fluid touchpad gestures introduced in Lion. The GUI appearance is just personal preference, so there's no point arguing about that, but I actually like the flatter, simpler look in new macOS. Besides, in Snow Leopard, you have to use an outdated third-party browser like Firefox 45, which is a significantly worse experience than Safari 12. For me, its only real strengths are lightness and Rosetta.
I just find that, overall, while old versions are nice in terms of appearance and nostalgia, they're simply not practical for daily use.