ETFs tend to have very low expense ratios, and they can be more tax efficient than mutual funds because they are able to sell holdings without generating a taxable event. This could be an advantage for taxable investors. However, brokerage commissions are charged on the purchase of ETFs, and for small and moderate purchases these commissions can overwhelm those other advantages. No-load indexed mutual funds typically have no purchase fees. However, if you are investing a lump sum (as, for example, when rolling over an established plan such as an IRA), an ETF may be an optimal choice.