mp3s
I experimented with a few higher resolution things from places like Chandos and Gimell but could not hear the difference.
I don't think God made me to be an audiophile.
I'm increasingly finding I get my most pleasurable listening experiences via the iPod. Even with inexpensive earphones I get a much better sense of the separate instruments than on my main system. What started as a way to listen to music in the early morning at a sensible volume without waking the neighbours is becoming a preferred way of listening. The only thing that stops me doing it all the time is a) gets a bit wearing on the ears after a couple of hours; b) as I move round the house the wire inevitably snags on something and yanks then painfully from my ears.
I recall a friend in the early 70s, who was much more knowledgeable about music than myself, being a bit dismissive of the enthusiasm of my fellow listeners for hi-fi (not that we could afford it!) - he maintained that someone really keen on music would happily listen to a 78 rpm, hearing through the imperfections to the music.
Though I can't deal with badly distorted records or poorly transferred CDs, I've increasingly come to see the wisdom of his view.