I have almost the same dilemma except that I don't have the choice to stay with my parents to assist them in their time of need.
My pop taught me that sometimes family is all that you have left,he has always been there for me just like my ma,when I lost my apartment because the rent went from $750 a month to $1500 a month he didn't even hesitate, he said "get all of your stuff and move in here".
I think that one of the main contributors to the current state of the world is the lack of family values.
People will kick their kid's out of the home as soon as they can, those kid's don't hesitate to put those parents in to some cold uncaring often abusive home.
Who needs you more?the army or your family?