Perhaps favourite is not the correct way to define music to suit ones mood at any given time because it's transient.
Favourites become tired or even annoying if played too often. You know: the classic songs like Fairy tale of New York, Hallelujah, Stairway to Heaven etc.
The genre I revert to most often is classical, progressive, blues rock, jazz and world fusion.
The greats: Chopin, Debussy, Tchaikovsky, Dvorak, Verdi, Zeppelin, Floyd, King Crimson, Yes, Steely Dan, Hendrix, Santana, Dylan, Bowie, Queen, REM, et. al.