Ranked in these QuestionsQuestion Ranking
Pro Better default terminal
Cygwin's default terminal "Mintty" is far better than CMD.
Pro You can run graphical applications
It has X Server.
Pro Additional packages available via Cygwin Ports project
Con Many incompatibilities
A lot of tools don't actually work with Cygwin, and documentation is often sparse, so for many use cases, it's worth the small bit of extra effort to just run a full virtual machine.