What quotation from the poem "A Psalm of Life" is closest to your philosophy of life?

I cannot directly answer this question for you, as I do not know your own attitude toward life, but I can give you some ideas to ponder.
This poem's main theme is making the most out of life. Its words remind us that the actions we take in life can truly impact another. For example, look at the stanza below:

Lives of great men all remind usWe can make our lives sublime,And, departing, leave behind usFootprints on the sands of time.

This quotation would be fitting for a person whose philosophy is that is is important to use one's gifts, talents, and abilities to enhance the lives of their fellow humans. If, as the poem says, a person is "forlorn," one's actions can help another "take heart again."
Another important idea of the poem is the importance of personal action and achievement in life. The poem makes many references to the fact that a person's time in this world is limited, and it urges the reader to live his or her life with energy and zeal in the aim of fulfilling his or her ambitions or goals. For instance, look at the last stanza's reference to this idea of personal action and achievement:

Let us, then be up and doing,With a heart for any fate;Still achieving, still pursuing,Learn to labor and to wait.

These lines would be an appropriate choice for a person whose philosophy on life was to embrace each moment of someone's existence and use it to continually hone and enhance their skills and to achieve each of their desired goals.