Vanguard states that VOO is intended to closely track the returns of the S&P 500, a stock market index measuring the overall returns of the US stocks.
VTSAX exposes investors to the entire US equity market, including all the small, mid, and large- cap companies.
VTSAX requires a $3,000 minimum investment, whereas VOO does not require an initial investment.
VTSAX comes at a slightly higher expense ratio of 0.04%, while the expense ratio of VOO is 0.03%.
VOO has marginally outperformed VTSAX, and it tracks the S&P 500. VTSAX offers broader exposure and is more diverse. So, some may consider VTSAX to be a better option.