It's an interesting question, Everett. For me, the answer isn't so simple.

A lot of stuff, I compose in C - because I can hear in my head what the chord changes sound like: C to G, C to D, C to E, C to F, C to Am, C to Em and so on. So if I know I want a melody to go in a particular direction, that's they key I use.

I realize that a real musician could use a number system and do this in any key - but I'm not a real musician. smile

That approach is useful if I hear the melody in my head and just want to find a chord progression that will fit it. Sometimes though, I don't have a melody up front but, instead, develop it from playing semi-random chord progressions. In this case, it's often better for me to use a different key, precisely because I can't anticipate what a chord change will sound like. In fact, sometimes I won't even know what chord I'm playing until I figure it out after the fact. For instance, my dobro is in open D but I'll experiment with different fingerings on it without knowing what the chords are.

So, like most things, it depends.... smile

Scott