nothing beats a fully patched, properly configured os3.9 install on a 060 + rtg setup.
I also vote for properly configured AmigaOS 3.9 with all the patches on any classic Amiga machine.
I don't understand the people who say 3.9 slow. Actually it's faster when you remove all the eye candy, icons, backdrops etc and install the proper patches and devices. On top of that you don't have to deal with AmigaOS 3.1 limitations, like small hard drive partitions and bugs. AmigaOS 3.9 is the best OS for classic machines without PPC board.