DAA or DAD as primary tuning ?
General mountain dulcimer or music discussions
I'm sure you'll get lots of good responses to this question Don!
I can only answer for myself, but here an explanation of why, as a noter/drone style player, I tend to like playing in DAA:
https://dulcimer-noter-drone.blogspot.com/2009/02/why-i-like-daa-tuning.html
But DAd is a great tuning as well! With the addition of the 6.5 fret DAd becomes quite versatile. And there is certainly more teaching material for beginners available in DAd, much of it in chord style playing methods. Most dulcimer 'clubs' and workshop settings currently lean towards DAd tuning and chord/melody playing style. It's convenient to have everyone starting out the same with the same tuning and books, etc.
But you can really do whatever you like!
I think DAC is my second favorite tuning after DAA- it's in Aeolian mode which has got the 'lonesome' sound.

What will you do now?
lolol krazy kid stuff...