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Advantages of ETF (Exchange-Traded Fund) over Mutual Fund

1. There are minimal taxable capital gain distributions for ETFs because of low portfolio turnover. That contrasts with many actively managed mutual funds where the decisions of managers to buy and sell stocks trigger taxable gains.
2. Expenses for exchange-traded funds are far lower than actively managed funds. For example, the expense ratio of 0.77 percent for iShares Emerging Markets Fund compares to 1.5 percent to 2 percent on some actively managed funds.
3. Investors can sell their iShares securities at any time during the trading day like regular stocks. That’s more flexible than traditional mutual funds that restrict trading or add redemption fees to discourage excessive trading.

So in esence lower cost.

Advantages of Mutual Funds over ETF
You get the whole index- the great companies along with the poor ones. An actively managed fund might do better than an ETF in a tough market because of the specialized knowledge of the fund manager. Mutual Funds are for those who believe a fund manager can beat the market in the long term.