CodeIgniter over ASP.net MVC

Windows is perfectly capable of hosting Apache + PHP (and MySQL if you're going to use MySQL for your database). It may be less efficient than hosting them on Linux, but that's not really the point (and I haven't tested it with a command-line Windows Server 2012 installation, so I can't be certain of the efficiency). I would be more hesitant about using IIS with PHP/CodeIgniter than I would be about using Apache on Windows.

I wouldn't choose to setup Windows servers in the first place if I wasn't using ASP/.Net, but if I had to use a Windows server, it wouldn't be a reason not to run Apache + PHP.

The difference in performance level from using an amp in Windows and Linux is huge, that's why I think it's a decisive factor.