401k

Index funds are the most consistent performing, lowest expense way to invest. It's like betting on the casino instead of betting on the next hand at the blackjack table in Vegas.

All the 2040, 2045, 2050... funds do is adjust the mix of your money invested in stock market, bond funds, money-market. The farther away the target date, say 2060, the more of your money invested in stocks and the less invested in bonds. Someone can accomplish the same thing by just readjusting the stock/bond balance every 5 years.