I am alas unable to sound any musical instrument.

But I like sounding
off about music!
I think you cannot have a favourite piece - it is almost meaningless. But also I think there is no piece, no music that bears too much repetition. You hear something again you may hear more, if you hear it too often you are hearing less or not hearing at all.
So is it open to give several pieces?
Sounding off: I think many performers, most these days, miss a bit of the point of pieces thinking they are extracting the last ounce of expression from them by playing them too s l o w l y. It has been proved by programmes and recordings that the length of performances has notably increased over decades. I felt this for the Gould-Goldberg on the first page of this thread. Though towards the end either he quickens or I got used to it. However I would bring a prosecution against Claudio Abbado for the murder, a long drawn-out one, of Johannes Brahms and Felix Mendelssohn.
For many pieces we may be a bit attached the the moment we first heard it, whether this is associated with anything else or not.
OK OK I'll get to some sort of answer. Many many years ago, almost by chance as a young green student passing by the Oude Kerk in Amsterdam I saw there was an organ recital and went in (there was if I remember as often in organ recitals not much more than a handful of listeners) and was taken aback by the piece I give. I committed to memory then the name of the piece (though it was many years till I worked out what it meant) and of the organist, who I presume was then only moderately famous (it was about the time, oh dear, though not place of this recording). I recently acquired ten discs of his of Bach organ music, but if there can be a 'favourite', something outstanding somehow in it, I can only say, purity, this is it.