D-flat major
D-flat major is enharmonic to C-sharp major. In music for the harp, D-flat major would be preferable, not only because harp strings are more resonant in the flat position and the key has fewer accidentals, but also because modulation to the dominant key is easier (by putting the G pedal in the natural position, whereas there is no double-sharp position in which to put the F pedal for G-sharp major).