Well, this is a tricky one.

Sony by itself doesn't do as much games as Nintendo does; most of them are 2nd and 3rd parties. Of course that the PS exclusive games have amazing songs: 'Moon Over the Castle' of 'Gran Turismo' by Polyphony Digital; 'Metal Gear Solid Theme', 'The Best is Yet to Come', 'Way to Fall' from 'Metal Gear Solid' saga from Konami; 'One Winged Angel', 'Eyes on me', 'Melodies of Life', 'Suteki Da Ne' from Final Fantasy and 'Simple and Clean' and 'Passion/Sanctuary' of Kingdom Heart series by Square-Enix; 'Zero' from 'Ace Combat Zero' of Namco-Bandai and many, many others of which i can't really count but most of them appears in 3rd party games or are just songs made by artists and putted inside the game.

However, made by SCE(I/A/E/J) or any other internal team; there're just a few i could remember. 'You Were There" from 'Ico', the music from PaRappa The Rapper, LocoRoco and Echronome; if they keep the song, the music background of LittleBigPlanet it's also nice and relaxing.

However, this little list at the end doesn't compare with the quantity of the same quality that Nintendo have. The music from Super Mario Bros. it's just classic; the same for Zelda, Metroid, Pokemon (Oh zeus! I still remember that midi-song on the opening of the first pokemon!), F-Zero X, Star Fox, Fire Emblem.

At this point, Nintendo wins without doubt