THE BATTLE between the world’s two largest exchange-traded funds has reached a pivotal second. On February 18th VOO, an ETF monitoring the S&P 500 that’s managed by Vanguard, a large passive-investing agency, took the crown because the world’s largest. Days later SPY, an ETF managed by State Avenue World Advisors, one other big, reclaimed it. Each funds boast belongings of over $620bn.