Each different tool has its own strengths and benefits.   If you are comfortable with php and mysql configuration and setup then do down that path - if you are MS SQL - IIS person the DNN is the place to start your investigation.

Personally, i found wordpress less than ideal as a CMS - with integration of new elements somewhat messy and hap-hazard.
If you are looking for a web content layout tool then its not bad - but if you want additional functionality - shopping cards, forums etc then you should look elsewhere.  Having said that its strength is its templates and layouts there are literally millions of them.

PHPNUKE is pretty much to php what DNN is asp.net .... It has a good following - but its somewhat of a challenge to configure and maintain.  While I have seen it running on windows system it is most ideal for linux based systems, 

DNN is easy to install and configure and its module system is easy to work with - on asp.net it is without a doubt the best free choice currently available,

Of the 3 DNN is by far the most end user friendly out of the box - and its incredibly flexible.