What advantages do index ETFs have over a comparable index mutual fund against the same benchmark?

Or, to ask another way, is there any reason to prefer anything other than Vanguard's Index500 vs anything else attempting to replicate the SP 500? (I call out the Vanguard fund because the fees are very low, .14% iirc.)

Vanguard also provides equivalent ETFs - VOO has expense ratio .04%, vs VFINX .14% - basically the ETF is like the admiral class shares ($10k+ investment). https://advisors.vanguard.com/VGApp/iip/site/advisor/investm...

Mutual funds: recurring investment of any dollar amount (fractional shares). Minimum initial investment required. Trade once per day, beware loads, fees, and expense ratios

ETFs: buy or sell one or more whole shares, trade throughout the day, beware trading commissions and expense ratios.

As others have mentioned, there isn't really much of a difference (apart from fees) when you're thinking about it as a vehicle for long-term holdings. Most of the time, 401k plans will not let you hold ETFs - they only let you hold mutual funds. Mutual funds usually can't be traded intra-day. You place your order and they buy/sell at the stated NAV on the close. ETFs can normally be traded intra-day. Again, ex-fees irrelevant to a truly long-term buy-hold-rebalance portfolio.

The SPY ETF is 0.0945% per year, although you still pay the broker when you enter or leave the position.

Vanguard's prices are great, especially if you get into their top-tier $10,000+ accounts. But ETFs are competitive against Vanguard in my experience.

Of course, Vanguard also offers low-cost ETFs. As long as you go with a mainstream option, I don't think you can go wrong.

ETFs trade mid-day instead of just end of day. You can only buy unit shares (but the unit price is typically far lower than mutual fund minimums). Those are really the only differences I know about.

Aside from fees, the trade price is different. ETFs have intraday prices while index funds have a NAV that settles after close.

None that I know of. ETFs are just easy to buy and tend to have low fees.

And maybe two index funds from different companies. If you really want to not have a single point of failure, use two different brokers.