A Comparison Of S&P 500 ETFs: SPY, IVV, And VOO (read full article here)
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Summary
SPY is the largest ETF, but its expenses are over double that of IVV and over triple VOO's fees, while they are also S&P 500 ETFs.
SPY has much higher trading volume, but with such tight spreads, only large investors and high-speed traders should need that liquidity.
SPY may also appeal to covered call option sellers.
While VOO is likely the best ETF choice, the best selection may depend upon what ETFs are commission-free at your broker, and some mutual funds offer lower fees too.