VTI or VTSAX?

Tit for tat between the two. Basically the same investment so if VTI has a commish associated with it just buy VTSAX.

I remember reading something about the ETF being more tax efficient than the mutual fund because it doesn't pay out dividends but keeps them invested within the ETF share price. Same intrinsic value but more tax efficient, in exchange for the risk of intraday trading (having to accept potentially less than market value on the bid/ask spread).

Vanguard has some patent on this dual structure for the same underlying fund, I'd check their blog for clarification. There's definitely a difference though.