Though I use XP & Solaris at work and Mac OS9.2 at home I would have to say...
MAC OS 10.2 and above, hands down, but...
BeOS WAS the best and I would still run it if my wifes laptop was supported fully (though I might receive a beating).
I haven't been fortunate enough to be able to build (for a resonable price

) an Amiga capable of AOS 3.5/3.9

and I don't have access to Morph (and it's killin me)
Yeah (sighs)... BeOS (sighs again)