I only clicked on this thread jjust now so it has been an interesting read all the way through.
Favourite sounds have changed from time to time in my life. At the moment I think that I'd choose bird song on a May or June Sunday morning, when there is little traffic around and I have my hearing aids in, turned up if necessary. Being able to relate different songs to names of birds makes it more interesting. When my great-grandchild arrives early next year, I dare say that a favourite sound will be the ones he/she makes.
I suppose I'll have to give Synthetic Dave a mention!!`