Hey hey hey....where's Macintosh? haha, but I use Linux/Windows/Mac Best of all worlds, but I mainly use windows for Photoshop/Dreamweaver (these can be found for Mac too, but windows is easier to use for me). Linux...I guess GIMP is ok for banners..etc..and you can do scripting in Linux too. Depends on what you like.
There is no best. All the platforms are good as long as you know how to use them and the programs on those platform meets your needs. For some of us, we just use multiple platforms to accomplish what we need. I guess if you are talking about using desktop based application to develop sites, personally I prefer Windows because there are more programs available for it. As for deployment, depends on which language you are developing in, if it is ASP and ASPX then it is a no-brainer, Windows is your baby. If you are doing PHP or Perl then most probably Linux. If they are just static or Flash based then either one should do the trick.
I'd agree with Windows simply because I adore Dreamweaver and don't see the point of running a Windows-native program on Linux. Besides I hate the GIMP too with a passion. It's worth trying Linux out though to see if it meets your needs for web development.