The SPDR S&P 500 ETF (NYSEArca: SPY) is the largest and oldest exchange traded fund, but that doesn’t mean you have to automatically look at this fund to track the S&P 500.

Of the three ETFs that track the S&P 500 index and have a 10-year track record, SPY is the worst performer, reports Eric Balchunas for Bloomberg.

The iShares Core S&P 500 ETF (NYSEArca: IVV) has outperformed SPY by an average 0.05% on an annualized basis over the past 10 years. The Guggenheim S&P 500 Equal-Weight ETF (NYSEArca: RSP) outpaced SPY by 2.27% over the past 10 years. [Equal-Weight ETF Still Beating the S&P 500 a Decade Later]

SPY, unlike many of the newer ETFs registered as a 1940 Act Regulated Investment Company, is structured as a unit investment trust, or UIT. Consequently, there is a slight cash drag as dividends can only be reinvested quarterly, whereas open-end funds can re-invest daily. Moreover, UITs can’t lend out securities and collect fees to help bolster total returns, or use index futures.

However, institutional investors favor SPY because of the attractive liquidity aspect – about 83% of SPY is held by institutional investors, whereas 51% of IVV assets are held by institutions.

“Large institutions moving tens of millions of dollars will likely prefer to use SPY,” according to Morningstar analyst Michael Rawson.