I have had some of the old electrets, nice detail, but lack bass. the pro4aa was very popular but sounds wonky by todays standards. the pro4aaa (vintage) is ok but still kind of dull by modern standards. the hv1a is a very nice vintage open air can.
for modern koss, i like the pro4aaat best (still have it). the dj100 has the most modern, consumer friendly sound
most koss cans need a good amp