The first GUI I would have used would probably have been Windows 1.0 on one of those old amber monochrome screens. I have virtually no experience with macs, though the mac GUI always looked and worked better than the windows one. The windows GUI always looked very ugly and cumbersome with all of the configuration scattered all over the interface, located in obscure programs or only accessible via the registry, right through to XP and it's cartoon themes. Out of the most modern GUI's KDE is still looking good, but it's just so bloated (C++).

Fast clean lined GUI's seem to be a thing of the past, it's all about cosmetics and effects now, even in the Linux world.