In order to live a happy life... Experiencing happiness (vicariously through others or not) involves the self one way or another because you are the one who is feeling it. Note that this does not address what the source of happiness is; I am merely saying that whether it is taking care of others or taking care of yourself that leads to happiness for you, ultimately, it is you (the self) who is experiencing it (others could be as well).
In my honest opinion, others are more important. I think making myself happy is okay, but making others happy is better. What is the point of being happy when you cannot or do not share it with others? Or, how long can you remain feeling happy when you know that others are not? As many people have pointed out, the answer is not strictly one or the other; there is a golden mean for everything.
Take care of others by taking care of yourself; take care of yourself by taking care of others *_*