I always go back to OS 3.1,
I guess it's the speed thing and my Amiga always runs best on OS 3.1
At the moment I have downsized my hard drive as well so space is a small factor as well.
Having said that 3.9 seems to have issues with my accelerator card.
But even on other setups I have had in the past I always end back on OS 3.1
