It's really hard to pick just one, and I have so many favourites for so many different occasions/emotions. Probably the one song I could listen to on repeat for forever though is Yesterday by the Beatles. Was one of my Nan's fav songs before she passed so it has a bit of a special place, but I just seem to have a connection to the words/melody of the song as well, and I really love the whole vibe of it. It's just one I don't think I'll ever tire of.