Does the Mother chose or the son?
When my niece got married her husband chose, yes HE chose, Love Me Tender. He chose it because he was born the day that Elvis died, his Mother went into labor when she heard that Elvis had died.
Even sweeter, he's a musician, and for the Father/ Bride dance he recorded with a full band a lullaby that her father, also a musician, had written for her when she was a baby.
SO my point is, I think the son usually choses, but if you`re chosing something yourself, pick something that is very special to you.