What's the best ? My friends say "Linux is the best" why ? because it is free ? what do you think ?

Anything open source is usually better than commercial software simply because it's free, community-based and driven, and more frequently updated [thus more secure].

Linux is definitely better than Windows for servers. It's faster and a lot more secure, and easier to manage.

Windows is easier for everyone at the present time for desktop computers, but that's soon to change with better Linux desktop operating systems such as Ubuntu.

I would go with Windows because Linux doesn't support my programs, such as Photoshop and Macromedia, and I also like to play games on my spare time.

At my home PC only windows (Vista)
But at server i prefer Linux

Yes, linux is much better for server. But for a personal / media computer I choose Windows.

As Linux is free, most servers in world use Linux, but windows is more populer among PC users.

The best combination IMO :

Windows XP on personal computers,
and Linux for web servers.

I like Windows Vista ultimate on personal computers
and Linux for web servers...

I used to only use windows, but switched to Ubuntu Linux a few years ago. I wouldn't go back now. I have still have a windows partition, but don't ever boot into it. I still work on Windows machines sometimes, but it only makes me realize how much better linux is.

If you aren't very computer literate or want to play new computer games than I would suggest windows, but otherwise something **nix based is way better.

Well i like them both and i also use them both, i'm using Windows XP and Vista and Novell openSuSe Linux. These and Leopard OS X are my favorite Operating systems out there..