ETFs make some sense in taxable because non-vanguard ETFs are more tax efficient than non vanguard mutual funds (vanguard has a patent that allows both their ETFs and mutual funds to be equally tax efficient), and if you want to tax loss/gain harvest you can have a better idea of what you loss/gain will be when you sell instead of not really knowing what the sale will close at at the end of the day. Neither of these are advantages in an IRA, so I would just go with mutual funds. Some countries also have better ETF options than mutual fund options (like Canada, I think), but in the US that's not the case.
