I learned in DAA for one day and then switched to DAD. I think DAA is considered more traditional, but DAD is more versatile so it depends on what you want. I just buy individual strings at the local music shops (10, 12, 24-gauge for DAD). I also use a capo a lot and, in DAD, I can get the keys of D, Em, G, A, and Am. I've never used a noder & I strum with those big lightweight guitar-type picks (the big, bulgy-triangle ones). I'm a notorious "cross-stringer" of melodies, so it doesn't bother me that the melody strings on DAD don't go down as far--heck, I'll play melody on the bass strings if I have to--but both of my dulcimers have pretty good separation of tone among the strings so notes played on drone strings are still audible.
A dulcimer strung for DAD can be retuned easily to CGC (key of C), DGD (G), and DAC (D minor), and probably others, all of which are fun to play with.
Overall, I guess it depends on what kind of music you want to learn and how sophisticated you want to get.