I chose VTI over VTSAX. It is slightly more flexible since it trades like a stock vs daily pricing on mutual funds. Not that I day-trad it, but I like to know what the exact price is when I buy. If I buy at 10AM, who knows what will happen by 4pm closing?
I grappled with the question of VTI vs. VTSAX at length. I did a bunch of research to find out what the main difference is. Nebulous comments about VTI being more tax-efficient appeared unsubstantiated. The only difference that seemed to come up over and over:
VTI: slightly more complex to buy (if you don't have a history of buying stocks), cannot directly buy fractional shares, but you know the price you're getting it for.
VTSAX: slightly easier to buy (Vanguard allows automatic investing with their mutual funds, not so with ETFs), you can buy fractional shares, but you don't know the exact price you are getting it for.
The advantage of the ETF is eroded in non-day traders (these are a buy-and-hold for most of us, so trying to time the trade to get a low intra-day price doesn't make sense for most long term investors).
In summary, the only differences: VTSAX is more convenient AND it allows you to buy fractional shares (this lets you put ALL of your employees to work).