I think at the end of the day it all comes down to what you have in mind.
Wordpress allows users to sign up for blogs and get their unique URLs on your server. And Pligg is an excellent Digg clone social networking platform. It is a high scalable yet demanding social networking platform.
But when it comes to choosing a Blog, Link Directory and review site you want your CMS to be highly scalable, flexible, and easy to use. At the end of the day, it all comes down to your taste. I personally like WordPress as it allows to host others’ blogs for free.