Sukiyaki is as iconic a song as there is Japan; it's the number one performed song in Karaoke bars across the country, as we found out to our cost when we went to one in Miyazaki. All our Japanese friends inisisted on singing it in Japanese and English, and afterwards in the car on the way home; I can still see the cheesy 60s video playing in my head like it's on a loop..........
I'm not sure that I have a favourite, my choice changes with mood and a zillion other factors. If I do have one, it'll be Your Song, by Elton John. It's the lyrics, magical.