I mostly use DADD (double melody string for volume, of course) for its versatility, but I suspect that my playing style has been "bastardized" by too much contact with fiddles and mandolins. I can capo it to E minor, G major, and A major/A minor (depending on whether I use the 6 or 6+ fret).

A lot of people in my area (Houston) use GDGG or DAAA, especially for gospel songs, but I don't usually bother to retune because it doesn't improve the range of frets I can use. I tune down to CGCC for C major tunes, and once had to tune to, um, BbF[?]BbBb to play with a bagpipe (I was amped). It was pretty awful.