Great question,
I would have to say Piano for sure. We had one in the house when I was growing up. My mother, bless her soul, played everyday, never had a lesson in her life, played by ear, self taught. She could just pick out a tune and just start playing, natural gift. As I was always running around the house and she would asked me if I wanted to sit down and learn, I always said no, I could not sit down for any length of time. I look back at it now and wish I would have done it.
It's funny, now I get the same response from my son when I ask him if he would sit down and learn the guitar.
Anyway, Keyboards, Hammond Organ would be cool.
Gary B)