The three biggest ETFs in the world right now are the Vanguard S&P 500 ETF (NYSEMKT: VOO), the iShares Core S&P 500 ETF (NYSEMKT: IVV), and the State Street SPDR S&P 500 ETF (NYSEMKT: SPY). Combined, they manage a whopping $2.27 trillion. Since they all track the same index, it could be assumed that they're all virtually interchangeable. At a high level, they are. Over the long term, you'll get about the same performance. But there is a way to potentially squeeze a little more juice out of the turnip. Wi ...