SPDR S&P 500 ETF Trust (SPY)

SPY is the most liquid equity instrument globally, with 80M+ shares traded daily. Launched in 1993 as the very first US ETF, it holds $590B in AUM under State Street management. Despite a higher expense ratio of 0.0945%, SPY's unparalleled liquidity outperforms VOO and ensures minimal bid-ask spreads for high-frequency traders and institutions.