As a noter player I like DAA best. I like the low melody note. I will sometimes set the noter aside and play harmonies of 6ths on the outside strings. Then the 6+ fret is a real asset, because the correct low harmony note is available. If I want lots of chords, I play guitar. 
I have a Feather Wren which I keep tuned in GDG for a couple reasons. I tried it in GDD (DAA up three frets) but it buzzed. It needs either heavier strings, higher action, or a little touch-up to the frets. Also the fretboard is too thin to easily allow noter-style playing. So I play it fingerdance/chord style for a change of pace. It is an excellent travel instrument, small (fits in my carry-on or backpack), lightweight, and quiet enough I don't worry about annoying people on the other side of sometimes-thin walls. In fact, my wife and I are planning a little trip in a couple weeks and I will take it with us.
My first dulcimer is DAA. To have near me; I got a backpack dulcimer... the gentleman said let me tune this GDD...okay. I got a feather dulcimer for trips...the gentleman said you'll like this tuned GDG. Soooo, if DAA and DAD are primary, why was the novice steered to other tuning. They both sound terrific....although the feather is a stinker to keep tuned. Explanation?
