I have both Australian and US index funds in both taxable and my SMSF.
In my taxable accounts, I am heavy on Australian funds - I want income and franking credits and I don't have to sell shares.
In my SMSF, I went high on US index funds. This was a more deliberate choice. This account will be tax-free and US shares provide way more capital gains than Australian ones. Up until now, this has been working well for me. Since 2016, my SMSF is up a million dollars and most of these gains are unrealised capital gains and will be tax-free.