Yes, I have an opinion on this subject. People have different likes and dislikes. This is important to remember when talking about subjective things. People approach things from different angles, and can even use the same words to mean completely different things! The qualities I value may not be shared by every one.

Firstly, I enjoy hearing music. I do not enjoy having my ears assaulted by harsh, abrasive, forced sound (unless that is what I choose to listen to).

Secondly I like to hear as much as I can of what is recorded. I don't want the system to get in the way.

Thirdly, I like my sound clean, tight deep and rich.

I have worked on valve and transistor PP and SE output circuits. I have also heard some pretty exotic (SE,PP &OTL) gear.

I became aware of a subtle difference in the sound of push pull and single ended amplifiers, which I have explored further in my own designs.

It is quite easy to loose this effect in the "valve sound", and also in the general indifference which constitutes most gear at the moment, but it is there.

I have also come to realise that it is not only a valve amplifier phenomenon.

In the course of my investigations I have found to my surprise, similar effects in transistor amplifiers, and also cables.

What I hear when switching from PP to SE in any situation, can be described as:

A increase in absolute transparency

A slight removal of grungyness from the sound

Voices tend to move backwards and become less in your face

The subjective noise floor seems to become more black

Small print

I must state at this point that this is my personal theory. It is what seems the most obvious explanation to me at the moment.