I'm curious of peoples different opinions on the different web servers. I currently 3 of my 32 websites run on a shared IIS server. I'm debating if migrating them to a linux server is even worth the trouble. I have no limitations or problems with the IIS server they are currently hosted on. So by your poll results and thread comments I'll decided if it is worth doing.
The only real reason to use IIS is to run microsoft items; such as ASP (.NET). For anything else I would recommend a Linux based server. It will use far fewer resources and will almost always be cheaper.
if u are more proficient with window, iis isn't a bad choice. Else stick with apache. wndows base is more prone to virus attack.
Think about what you've written first. Is there any reason at all you want to migrate? Are the IIS Servers slow, or don't work, or simply too expensive compared to the Linux boxes? Why do you even care what people here on DP think - they do not know what your sites are and how their functionality under IIS is.
Quoting IIS's command line admin interface as an advantage is being very liberal in its favour. Also, another well known disadvantage of using IIS/Windows is that the boxes often require reboots after patching. Usually, the only time you need to reboot a *nix box is if the kernel has been changed, which is quite rare. However, as the others have said, if you have real tangible, imposing reasons for migrating then do it. Otherwise, why not just leave them as they are running fine.
Personally, I prefer Apache, and I prefer Linux. You can run Apache on windows, so that is why I mentioned linux as well. Like others have said, Windows is mroe vulnerable to attacks, and is less secure. It's also more memory intensive. Windows has a lot of overhead to work with. Since it has a GUI and more, a lot of performance and RAM gets ate up by that. Also, you have to pay for licensing costs. Linux is free, and since it is command line, it doesn't have a lot of memory and resource overhead. I prefer linux. I'm also testing the Lighttp server, because it's compatiable with cPanel. I've been testing it for performance and see if it can outperform apache.
I can only recommend one thing that if you're going to host a huge traffic website, I would recommend IIS, otherwise apache is best