I personally have DX because I often read pdf-s and a larger screen is important then. Kindle 2 is smaller and easier to carry around (it is more convenient for commuters and such).
Here are some links to help you decide:
http://ireaderreview.com/2009/05/05/...x-vs-kindle-2/
http://kindledx2009.blogspot.com/200...kindle-dx.html
http://blogkindle.com/2009/06/kindle-dx-vs-kindle-2/
http://geekmalaya.com/wp-content/upl.../kindle-dx.jpg