The differences are that homebrew installs to /usr/local by default, doesn't keep track of package versions, and doesn't install its own versions of libraries that come with OS X (and therefore might be screwed up by an OS update). These are all Really Bad Ideas, which make homebrew technically inferior to macports, and less stable. However, they also make homebrew really simple, so it's much quicker and less cumbersome to use. Almost the definition of quick-and-dirty.