Just my 2 cents,
It appears they track different indexes, both of which are meant to be all encompassing of the US market. ITOT tracks the S&P Total US Stock Market.
Anyways, according to a M* growth chart, VTI gained 7.4% per year for the last 9 years while ITOT gained 6.9% per year for the last 9 years. On a 10K investment, that is about 800 extra bucks for VTI. Possible reasons may be higher expenses for ITOT (granted now they are quite close, I'm not sure what the difference was in past years) and ITOT has a slightly smaller Small Cap position. Plus they track a different index.
I'll leave it to you to decide what is best, I'm merely passing on a tidbit of information to you.