SPLG tracks the S&P 500, the same index followed by SPY, VOO and IVV. Unlike SPY, which is a unit investment trust, SPLG is an open-end fund, so it can reinvest dividends immediately instead of holding them in cash until the next distribution. Its expense ratio is well below SPY and comparable to VOO and IVV, so differences in long-term performance between SPLG, VOO and IVV are expected to be very small. SPY has deeper trading liquidity and the most active options market, while SPLG is more often used for buy-and-hold investing. For S&P 500 funds, the choice usually comes down to brokerage platform, trading costs and personal preference rather than differences in holdings.
