SPY

SPY is the best-recognized and oldest US listed ETF and typically tops rankings for largest AUM and greatest trading volume. The fund tracks the massively popular US index, the S&P 500. Few realize that S&P's index committee chooses 500 securities to represent the US large-cap space - not necessarily the 500 largest by market cap, which can lead to some omissions of single names. Still, the index offers outstanding exposure to the US large-cap space. It's important to note, SPY is a unit investment trust, an older but entirely viable structure. As a UIT, SPY must fully replicate its index (it probably would anyway) and forgo the small risk and reward of securities lending. It also can't reinvest portfolio dividends between distributions, the resulting cash drag will slightly hurt performance in up markets and help in downtrends. SPY is a favored vanilla trading vehicle.