Woooo...tough choice!!
Favourite instrument: guitar, although the sound of a well played B3 can't be beat.
However, my favourite sound, and I know this is gonna sound odd, is from the Gaelic pipes as played in the "Riverdance" production...now that's a haunting sound.
In keeping with the guitar/B3 thing, my favourite songs & tones, off the top of my head would be: Summersong, Whiter Shade of Pale.(Hey I know it's old...but it's classic)
Just my thots.