Well, obviously a matter of opinion, nonetheless post the one what you think the best:
I will recommend Faure’s Apres un reve. Based on an Italian love poem, and translated into French tells the tale of these lovers that meet while they sleep and escape the real world to meet in this world full of light, and then suddenly he/she awakes in a sad manner. In my opinion is possible the best love song ever composed (and by composed I meant musically speaking, although the lyrics are pretty good). The composition is very simple, a female soprano singing the song just being accompanied by a piano/cello or sometimes both in the background.
Lyrics:
Dans un sommeil que charmait ton image
Je revais le bonheur, ardent message;
Tes yeux etaient plus doux, ta voix pure et sonore
Tu rayonnais comme un ciel eclaire par l'aurore;
Tu m'appelais, et je quittais la terre
Pour m'enfuir avec toi vers la lumiere;
Les cieux pour nous entr'ouvraient leurs nues;
Splendeurs inconnues, lueurs divines entrevues...
Helas, helas, triste reveil des songes !
Je t'apelle, o nuit, rends-moi tes mensonges;
Reviens, reviens radieuse
Reviens, o nuit mysterieuse















