Identifying the absolute best Vanguard fund to invest in depends heavily on an individual investor's personal financial goals, risk appetite, and time horizon. However, financial advisors frequently highlight broad-market index funds—such as the Vanguard Total Stock Market Index Fund or the Vanguard S&P 500 ETF—as exceptional core holdings because they offer immediate diversification, ultra-low expense ratios, and consistent long-term performance tracking major market indices across varying economic cycles.