This is a pretty intense question, but I will bite. I think I would have to say my wife. My mother is a saint, she is a kind wonderful woman. Give the choice, I wouldn't want to lose her at all. She has also live a full amazing life though. It would be sad if she were to pass away, but I know that she made the most of her time on the Earth and she would probably pass away with no regrets.
My wife and I still have a lot of time ahead of us(I hope). I want to spend as much of that with her as I can. For me, it is a pretty simple choice. If I were younger, my answer might be different.