Fingering may be much easier in some keys. For example, less experienced
fiddlers often gripe about playing in the key signature of Eb. Tone quality
can be affected by the more difficult fingering, too.
Also, the sound of an open string is different from a string where the
fiddler has a finger pressed down. G, D, A, and E are the usual tunings for
the four fiddle strings.* So the key signatures of G, D, A, and E can use
those strings as open; and thus may have a clearer, more ringing sound than
* Different tuning patterns may be used for certain effects, or styles of
Other instruments have different strengths and weaknesses. Even playing the
same type of instrument with a different range (e.g., soprano recorder
versus alto recorder) may be much harder.
The easiest thing to do is to have a player of your desired instrument give
the tune a test drive and offer comments to you.