When I was in university at some point I said to a good friend of mine "When I grow older and I have a house I will have one computer with each platform" Well I am older now and I have a house, and wife, and kids, and spare computer parts (doesn't everyone have them), lego, tons of lego, although not enough. But the one thing that I also have is accomplished my dream of having one copy at least, of each platform, so not only I have accomplished my dream but over accomplished it, because in reality I have multiple copies of many platforms.
Back then in Uni i was really refering and having: 1 linux, 1 Windows, 1 Mac at that time people would ask me why a Mac? and not everyone would know also that there was something call Machintosh.... well those times certainly have change.. haven't they?
So which platform I prefer? I will say not OS/390 or AS/400 but maybe because I don't have enough experience with them, my experience with both of those platforms have been limited by access at times.
I declare myself O/S Agnostic.