There don't seem to be any concrete reasons for using one over the other as far as search results or other desired outcomes.  My personal preference is no-www, due to length.  The most important thing is to make sure you redirect to your preferred domain, and remember to set your preferred domain in Google Webmaster Tools.

[This article][1] gives a pretty good summary of the situation,


  [1]: http://www.sitepoint.com/blogs/2008/02/19/www-or-no-www/