In my opinion, Mac OS X (http://gswg.io#osx) provides the optimal development environment. Mac OS X combines a Unix-based operating system with a brilliant user experience, allowing you to make use of the vast number of Unix-based development tools without having to worry about system level intricacies and incompatibilities. Homebrew (http://gswg.io#brew) is an OS X alternative to Linux's apt-get, providing a simple and easy-to-use method for installing command-line tools.

Windows is useful if you develop on the Microsoft stack (.NET, C#, and so on). However, Mac OS X is better suited to frontend development. Since, in addition to Unix developer tools, there are many powerful graphics and design...