Utilitarianism is flawed, but has merit. The Kantian philosophy of Innate Worth also has merit - although Kant essentially ended up acknowledging that mans innate worth came from him being useful - even as a lump of flesh that did nothing.
I believe that the Church of Jesus Christ of Latter-day Saints has the only true and complete philosophy - a philosophy without gaps or holes. This philosophy is based on what God has determined as utility, and recognized that not only are we his mortal creations, but we are all literally spiritual offspring - children of our Heavenly Father. As such, not only are we valuable because of what we do that mankind values, and because we serve a purpose even if we do nothing, but also because we are of a divine origin and have a divine destiny. In other words, our value is based on our divine potential - not necessarily as man sees it, but as only the Creator can judge it. And that value is not subject to the whimsical values of mankind. This value is based on an absolute moral philosophy dictated by the laws of God, conveyed by His prophets. Everyone has value only determinable by God. As we repent in our mortal bodies, and as we become followers of Christ - being baptized into His family and taken under his wing - and serve His will, we can reach our divine potential and completion. In other words, our value is not just in our creation and being, nor in our secularly determined utility to mankind alone, but because of our divine potential determined by the alpha and omega - the ultimate creator and determiner of value.