I didn't bother to vote until there was an AROS option, since I use (or rather test) AROS far more than the other options 
Ditto, I voted for MorphOS when it was added as it's what I'm currently using the most due to having two old Macs to put it on.
Now that AROS 68k is getting some long deserved loving if I was asked the same question in a couple of weeks my answer might be different.