The most important decision we can make is whether this is a friendly or hostile universe. From that one decision all others spring.

Multiple variations of this quote can be found, but the earliest one on Google Books which uses the phrase "friendly or hostile" and attributes it to Einstein is The Complete Idiot's Guide to Spiritual Healing by Susan Gregg (2000), p. 5, and this book gives no source for the quote.

A variant is found in Irving Oyle's The New American Medicine Show (1979) on p. 163, where Oyle writes: 'There is a story about Albert Einstein's view of human existence. Asked to pose the most vital question facing humanity, he replied, "Is the universe friendly?"' This variant is repeated in a number of books from the 1980s and 90s, so it probably pre-dates the "friendly or hostile" version. And the idea that the most important question we can ask is "Is the universe friendly?" dates back much earlier than the attribution to Einstein, for example in Emil Carl Wilm's 1912 book The Problem of Religion he includes the following footnote on p. 114: 'A friend proposed to the late F. W. H. Myers the following question: "What is the thing which above all others you would like to know? If you could ask the Sphinx one question, and only one, what would the question be?" After a moment's silence Myers replied: "I think it would be this: Is the universe friendly?"'