Getting your player ready...
Financial wonks often talk about exchange-traded funds as the next big thing. In December, they were the thing, at least for stocks.
ETFs are like traditional mutual funds, except investors can buy and sell them through the day like a stock. Last month, stock ETFs attracted $21.3 billion in new money, according to Lipper.
Traditional stock funds, meanwhile, saw investors yank out $2.1 billion. For bonds, though, mutual funds still reign. Tracking an index can be more difficult for bond ETFs than their stock counterparts, because some bonds rarely trade.
