VTSAX is the Admiral version and provides the lowest cost, but has a $10,000 minimum buy-in. The Investor Shares option, VTSMX, holds the same portfolio, but with slightly higher costs and a $3,000 minimum. He should use Admiral Shares whenever he can and Investor Shares if needed as a start. Once the account reaches $10,000, Vanguard will automatically switch it to the lower-cost Admiral Shares.
