The differences are bigger than just a race to the bottom in fees.  Here are five ways to dig deeper into the choices within the ETF universe that target emerging markets opportunities.  1. Know your 'Korean war' history.Last June, Vanguard transitioned away from the MSCI index standard to a FTSE benchmark for this ETF. That move eliminated exposure to South Korea, as FTSE considers it to be an advanced market rather than an emerging one. South Korean stocks, including Samsung Electronics, made up 15 percent of EEM assets, making it the second-largest country exposure behind China. The absence of South Korea is noticeable. Meanwhile, VWO has more exposure to Taiwan, Brazil and India than EEM.  These index component changes showed up in a significant way in performance divergence. In 2013 EEM lost only 3.7 percent, while even with a lower expense ratio, VWO declined 4.9 percent. That has reversed in 2014, during which VWO has been the stronger performer, with a 4 percent return through May 22 versus a 3 percent return for EEM.  2. Swap EEM out for IEMG.Investors should go beyond the two largest emerging markets ETFs. In fact, iShares introduction of the Core series emerging markets option compels an investor to take a look at the new but fast-growing lower-expense ETF within the same iShares family.  The iShares Core Emerging Markets (IEMG) came to market in October 2012 and has already gathered more than $4 billion in assets. Relative to EEM, IEMG has the lower net expense ratio of 0.18 percent alluded to above, but it also has additional exposure to small- and mid-cap stocks that are more tied to the local economies, including South Korea. IEMG's weighted average market cap is $38 billion, modestly below EEM's $44 billion, according to S&P Capital IQ.  In May, EEM has continued to lead the way, raking in $861 million in assets through May 22. But IEMG is second among all emerging markets funds, taking in $366 million, according to ETF.com data.  Read MoreThe biggest wealth destroyer in the market?  3. Stay small.There are many other ETFs that focus on one slice of the emerging markets investment spectrum, but there's added risk, as they offer less diversification.  For investors that want to avoid the large-caps inside IEMG, the SPDR S&P Emerging Markets Small Cap (EWX) is one such ETF, with a 0.65 percent net expense ratio. EWX's weighted average market capitalization is $1.3 billion, and its exposure to Taiwan (30 percent of assets) is much higher than the previously mentioned ETFs; India follows with 10.8 percent of assets.  4. Leave LatAm.Of course, if you want to increase your exposure to Emerging Asia, you might want to consider SPDR S&P Emerging Asia Pacific (GMF), which has a 0.59 percent expense ratio. This regional ETF focused on some of the fastest-growing emerging markets and eliminates Latin American exposure. This is a good thing when those markets are out of favor, but owning it thus far in 2014 would have caused you to miss out on the strong gains in Brazil.
Why did investors put $5 billion into emerging markets ETFs in April, after $12 billion in outflows in the first quarter?