- Moon Over The Castle because it's basically GT's theme song (or,
used to 
)
- Everything Must Go because that's the one that started everything outside Japan
Or
- My Favorite Game because that's about what GT has turned into, even GT5. They could even just put a remastered GT2 intro for GT6 buut alongside the old footage of real racing the could put, well, guess three times
Either way, I just hope it has something to do with GT's origins. Oh, and, slightly offtopic, From The East must also be in GT6! GT5 truly got rid of them legendary tracks of both kinds..