I would say of course Linux....but since it was not an option, I'll say Mac. Mac OS X is based on Darwin, which in turn is based back on BSD. What does this mean??It means you have the user friendliness of Mac with the power of unix. I have had the pleasure of playing with os X...and I might say I'm impressed. The absolute ONLY reason to use doze is for convenience.....and I don't mean laziness...I mean convenience. (i.e, I havn't got the rca-in working on my video card under linux yet, so I use doze when I need to watch tv). It's more of a backup.
All that to say my final verdict would be Mac....so long as you have osX