Funds are tax inefficient when they make large annual distributions (dividends, capital gains,...) because you have to pay taxes on those distributions annually and therefore you have less money left to compound. So bond funds, REITs, and balanced funds are considered the most tax-inefficient. For equities, value funds, equity income funds and managed funds can also be considered tax-inefficient. What is considered tax efficient then? Equity index funds (blend or growth) are some of the most tax-efficient investments you can find. They tend to have low dividends, and because they don't do a lot of trading (because they track an index), capital gain distributions are minimal. If you must have bonds in your taxable account, then go for municipal bond funds, their dividends are tax-free (though if you are subjected to the AMT, you might not enjoy the tax-free distribution on those unless you choose your fund very carefully).
So in order to maximize your tax efficiency, and if you have both a 401K and a taxable account, you would want to keep all your bond funds, REITs, balanced funds, equity managed funds, value funds and equity income funds in your 401K and keep only equity index funds in your taxable account. So let say you have a 401K with $50K and a taxable account with $50K. If you want a 70% stock / 30% bond allocation overall, you should have $30,000 worth of bonds in your 401K (30% of the total), you should have $20K worth of stocks in your 401K (which can be managed funds, equity income, value stocks or other tax inefficient investments) and $50K worth of stock in your taxable account (which should be tax efficient, like a total market fund).