I teach most of the DAN courses, but I try not to be biased.
I recommend every person (diver or not) be trained in at least a Basic Life Support course (First Aid, CPR, AED) whether provided by the Red Cross, American Heart, your Scuba Agency, DAN, or other.
I also strongly recommend that every diver be trained in at least Oxygen First Aid. DAN is one of the few accessible sources for this training.
DAN Divers Alert Network : Training & Education : Oxygen First Aid for Scuba Diving Injuries
It's no coincidence so many dive centers offer this course.
After you have those two under your belt, you might be in a better position to assess whether some of the other DAN offerings are appropriate for you.
I also recommend that every diver take their agency's Rescue Course.
Some of DAN's standalone courses like AED and Neurological Assessment are pretty narrow, and you might be better off finding courses that include these relatively short topics.
On the other hand, I think DAN's Basic Life Support for Dive Professionals (not limited to dive pros) and Diving Emergency Management Provider are excellent courses.