Picking either one is better than sitting in $100k cash.
That said, I prefer ETFs. If you want to rebalance or tax loss harvest, you can do that in one login instead of two. Let's say I wanted to realize losses from VTI (Vanguard Total Market) and switch to IVV (iShares S&P 500). I could login and sell VTI, and the credit for that sale is immediately available. I can then, immediately, buy an equal amount of IVV. One login, and I've switched investments from VTI to IVV (which is now $0/trade thanks to recent changes at Vanguard).
Mutual fund sales/purchases are handled after the market closes. So you wait the rest of the day before your sale of VTSAX goes through. The next day, when the cash is available (I think?), you can start the purchase of another mutual fund. And you then wait, in cash, until the market closes and you can buy the other mutual fund. ETFs, meanwhile, are sold/bought instantly.
Also, I think Vanguard offers ~1800 ETFs for $0/trade, but only offers it's own mutual funds for $0/trade. So there's more choices (like SCHB, ITOT) available with ETFs.