I am Amiga user since 1985, and the first time I saw the "miggy" term used for Amiga computers was on users forums, and the first thing I think was "WTF?". Really? "Miggy", come on!.
I not agree about that nickname, but anyway, I suppose some people think they're using a"loving" way to call the Amiga computers.
I just call "The Amiga" or "the 500, 1200...". If I am writing something about any specific model, sometimes y write "A1200, A500, A2000...".