I've always found DADGAD very usefull. The difficult bit is playing in a range of keys. It's OK for D, Dm, G, Am, Bm, Em, and Gm but can be difficult for C. Yoy realy need a good capo. As a derivitive I had Steffan Sobell build me a Cittern (5 course Bouzuki) to tune DADGD. Works very well.