I invested in SPY ...

SPY is the best-recognized and oldest US listed ETF and typically tops rankings for largest AUM and greatest trading volume.
SPX, the index is widely used as a barometer for the health of the U.S. stock market, representing roughly 80% of US stock market total value.
BlackRock iShares XSP is an exchange-traded fund designed to replicate the performance of the S&P 500 (Hedged to Canadian dollars).

I invested in SPY because of it's track record over the past 100 years. It recovered from many market crashes including the 2008 housing crash and 2001 dotcom bubble. However do your own due diligence, this ETF is for long term.