What difference does a few billion dollars make? Probably not much, at least when it comes to measuring exchange-traded fund inflows in 2012. Depending on who’s doing the counting, investors poured either $188 billion into U.S. ETFs last year (IndexUniverse) or $191 billion (Morningstar), according to recent figures released by both companies.

Either way, these numbers topped the previous all-time high set in 2008 of more than $175 billion (IndexUniverse) or $169 billion (Morningstar). Both companies agree that the final tab for U.S. ETF assets as of year-end 2012 was $1.35 trillion.

No matter who crunched the numbers, ETFs clearly are on the upswing among investors looking for low-cost ways to allocate their money across different assets and strategies.

Both companies said the SPDR S&P 500 ETF (SPY) took in the most assets last year, even if the actual amount differed––IndexUniverse put SPY’s asset haul at $15.77 billion, whereas Morningstar put that figure at $20 billion.

IndexUniverse said the Vanguard MSCI Emerging Markets ETF (VWO) and the iShares MSCI Emerging Markets Index Fund (EEM) both gathered about $10.5 billion in assets to place second and third, respectively. Morningstar flip-flopped the order, with EEM gathering $10.5 billion and VWO collecting $10 billion.

“People think that fund flows are accurate to the dollar, but they’re always estimates,” says Morningstar ETF analyst Michael Rawson. “That’s particularly true with mutual funds, but ETFs are more accurate.”

Rawson says Morningstar gets data directly from the fund companies. “We think we have the most accurate [ETF] database. But it could be that we’re missing a few funds, or that IndexUniverse is missing some funds, too.”

Dave Nadig, research director at IndexUniverse, says the slightly different numbers between the two companies is a methodology issue. "I'm pretty sure the main difference between us is that they capture January 1," he says. "They start a day later and end a day later than we do."

Fixed Income
One of last year’s big ETF themes was the burgeoning inflows into fixed-income funds, which was spearheaded by the Pimco Total Return ETF (BOND). That fund, which mirrors Pimco’s popular namesake mutual find and was the most successful U.S. ETF launch last year, took in $3.87 billion in assets (IndexUniverse) or $3.77 billion (Morningstar), enough to rank as the 10th-most popular fund in 2012 on both lists.

IndexUniverse says bond funds collected about $56 billion in assets last year, or roughly 30% of total inflows.