Due to my love of food, probably a food related business, e.g. cafe, as long as I didn't have to work in it every day.
I am assuming that the amount of money this business brings in, is not part of the question?
I have owned my own successful business for many years and while I enjoyed running this, I am now doing voluntary work, so at this stage of my life I would not really want to own a business despite my answer above!