whats is better to start a server on a windows,unix or lunix?
which one has more security?
which get less viruses?
which is better for programing and web design?

Linux Red Hat is proven to work well with Apache Server, PHP, CGI/PERL.
It is also less vulnerable to viruses if you update your system patches regularly or whenever new patches are available.

All the stated systems will not affect your programing and/or web design if applications softwares required are properly installed and configured except for Windows, PHP on window have lesser functions than PHP of the same version on Linux and Unix.

This all depends on what you want to achive. If it is just a stand alone server for web and e-mail then I would sugest Linux, but if you want it for a large userbase for security and easy of use I would suggest windows.

Windows provides forests and domains that help alot in the security of the clients.

I also beleave that windows is better for the user that just wants to use a PC for there day to day things.

If you are an advanced user, Linux could do well as long as you are willing to learn things all the time as linux is not that user friendly.

I personaly use windows, but thats just because I support a windows network. If I had the hosing space for a personal server, I would run Linux. (Stand alone Server)

FreeBSD (freeBSD.org) this is THE operating systems for servers.
i would say FreeBSD is more or less equal to a good linux Distro, but BSD is more mainstream (if that is important to you)

Both FreeBSD and Linux are Secure... but the actual security of your site will depend on how many mistakes setting up the web servers... for example, some people will make a new account like username ftp, password ftp for public downloading, but they forget to dissable that account for SSH logins... then anyone can SSH into your machine, and use it to send spam email. (this kind of human error is quite common)

Windows is the ONLY major operating system out there that has a problem with Virii.
Virii can only exist under certain conditions that do not exist in other Operating Systems (Unless a virus find a way to get root access (or guesses your root password)
SO ANYTHING except windows.

However.... you have to realsie that most people viewing your server may be using windows... so even though you are running Linux or BSD, you still need a virus scanner to prevent users from uploading virii for other windows users to download.

in my Opinion, Linux... but ive never developed in BSD or any flavours of UNIX.

so basically.... Anything Except Windows.

If you want a Commercial Unix OS, go for Sun's SOALRIS.

if you want a Free Open Source Unix, go for FreeBSD.

if you want to go for Linux, use either Slackware, or Gentoo.
Redhat is a more famous Server Distro... but its a little too bloated in my opinion, but maybe a little easyer to setup.