Which version of these operating sytems are we talking about?

I have to say that I like all of them, but for different reaons:

I like Windows for 2 reasons: It's really good for gaming, has both DirectX and OpenGL support, etc. The other and larger reason why I like it is because Microsoft really catered to the developers when they built it -- I have yet to see a development tool for any other platform that's as powerful as Visual Studio.

I like Mac OS X because it's very unified -- there's only one machine it runs on, which is great because Apple's designers only have to worry about one machine. Oh and I really like the UI.

Linux is cool because, well it's open source, and how much cooler can you get than that? But aside from that "reason", usually why I use it is because it gives me more power under the hood, so-to-speak. And the applications written for Linux far outnumber Mac OS X.

I've never used Unix directly, but I've used FreeBSD which can almost be considered Unix (well, not quite). I also like the fact that it's unified, which is perfect when trying to deploy applications, or simply trying to download that latest cool new program that I discovered.