The best way to answer this question is to quote EC-Council's CNDA FAQ:

"How different is the (CNDA) exam compared to CEH?

Except the title difference, the content of the exam is 100% same as CEH exam. There is no difference other than the exam title. You can use CEH exam preparation guides for this exam, too."

CNDA is for government agencies only. It was created to eliminate the stigma of hiring people with 'hacking' certifications, even though they desire the same skill set. So unless you work for a department within the US Government, and they approve the taking of the CNDA course, then you should take the CEH training instead. For those of you who work for the government and already have the CEH credential, you can be awarded the CNDA certification by filling out the Application Form (PDF) from EC-Council.