This question is so vague. How would the money be acquired? How would world peace be achieved? The money could come from a hacker who embezzles money from world banks, and world peace could stem from the establishment of a global dictator with absolute power. Without any strings attached and no shady methods, I would pick world peace.
World Peace. The only reason I'd need a bilion would be to feel secure for the rest of my life and it's kind of hard to achieve with wars and **** going around.
World peace. I really, really, REALLY hope that people voting for the money are kidding. Like material objects over achieving the ULTIMATE goal of humanity? Like do you know what we would achieve if countries stopped bickering and worked together? Poverty would literally be ended so promptly.