Good q.. This is an age-old Bogleheads debate: SPX or Total Market. SPX has a bit more juice- it's like the Major Leagues of the US while VTI is more expansive, incl minor leagues. More people pick SPX by far, one reason could be that stud cos IPO as large caps now so less need to hold small/mid. But at end of day you'd be fine in either ETF for long-term.