I have worked with Ektron for 5 years and DNN for 4. They really are different beasts but with some cross-over. In fact I may integrate them, but I am leaning towards leaving Ektron (unless certain things change).
Regarding Ektron
1. I personally don't like their templating model
2. I am not happy with their support
3. I am not convinced that they have a good QA process
4. I am not convinced that they value Usability Testing
5. I regularly run into bugs that sabotage my environment and take a long time to fix
6. Their code base appears to still rely heavily on legacy ASP
7. Their foundations do not seem strong to me. Instead of firming them up they appear to be chasing new features
8. They have a solid editor and good tools overall. For some businesses they are exactly the right fit
9. I believe that Ektron at the highest levels has very good intentions and is run by caring people
Regarding DNN
1. The structure of the system allows me create modules that can do anything. These modules can be moved around a page at whim.
2. Everything is database driven
3. Standards are being pursued
4. New and wisely selected innovations regularly find their way into DNN
5. Lacks a strong CMS solution (approval chains, versioining, etc.) I am hoping to find 3rd party modules to solve this or build my own.
6. The system is not proprietary, it's open source, so when I want to enhance something - everything is open before me
Summary: Ektron is a great solution for users without a lot of technical expertese. DNN is a framework in which I have tons of freedom and foundations on which I can build.