I still think on an A1200, 3.1 plus 8-color Magic WB and Magic Menu ToolManager Dock MUI capture the Amiga Look and Feel better than anything else.
Plus its fast, uses little precious chip ram, icons actually look like what they're supposed to represent, the "3D" look is consistent from the icons to the menu's to the docks.
It takes a fair bit of effort to get it going though, but thats part of the fun.
If you can''t be bothered than Classic Workbench.