For the diversified portion of countless investors' portfolios, the key choice has been ETFs vs. mutual funds for years now. For many investors, the choice boils down to this: Exchange traded funds tend to be cheaper than mutual funds. So shouldn't investors simply stick with ETFs? X

In fact, shouldn't you dump your mutual funds for ETFs?

You might be tempted to switch since many financial advisors and independent investment strategists now focus on using ETFs rather than mutual funds to build clients' portfolios. That's mainly because of cost, flexibility, transparency and tax efficiency:

ETFs cost less. Most ETFs have lower expense ratios than actively managed mutual funds. Expense ratio is the term used to show what percentage of your assets you pay annually to own a fund. The average stock ETF carries an expense ratio of 0.38% vs. 1.08% for the average stock mutual fund. For a portfolio of $100,000, that would be a difference of $700 a year. Be aware, though, that many index mutual funds now also offer low expenses ratios. And keep in mind that ETF expenses aren't confined to expense ratios. There's also bid-ask spread, which can be wide for lightly traded ETFs.

ETFs have more flexibility.ETFs can be bought and sold throughout the day, so investors can act quickly to take advantage of opportunities that arise or take their portfolio out of harm's way if the market takes a sudden bad turn. Orders to buy or sell mutual funds are executed only once a day at after the close of market trading. That's when their net assets values are calculated based on their holdings.

And, like mutual funds, you can place limit orders on ETFs.