I'm a little wary of the Cloanto 3.X ROMs and Workbench, but the 3.0 and 3.1 releases are basically the same as the Commodore ones. On my three A1200s I'm running a fairly standard 3.9 setup with BoingBags 1 & 2, the Euro update and certain other components that also feature in BB 3 & 4. I haven't installed the full BBs 3 & 4 though...
Important components (for me) that I have on all my Amigas to add to the standard OS:
And on my main A1200 I have the new layers.library too.