Hi, I've been an user of both. I wrote about Taskwarrior here: http://www.mostlymaths.net/2011/03/using-taskwarrior-instead...

I am using it more often than org-mode, mainly because it works very well in my Ben Nanonote, and org mode does not work as well.

It is very good, but org-mode is more flexible (as everything in emacs is) and covers a wider range. Tw is more like the "do one thing and do it well" Linux command line style tools.