R. wrote...
nee's can cook and take care of you. What can imouto's do? Be a pain in the ass.
While giving them pains in the arse as punishment for being a disrespectful imouto. And make them call you onii-chan when they suck your dick. Nee-sans have the downside of being old enough to be married or smart enough to be not interested.
But if given the choice I wouldn't be so picky to choose one over the other. Keep your options open.