The emerging markets theme seems to be the most popular around. But what is the best ETF to get you there?

Emerging markets have been seducing investors for the past decade -- high growth, big returns, and global economic domination are just some of the theme’s siren notes.

Retail investors were told they needed emerging markets exposure in their portfolios, and for a long time they mindlessly clicked “buy” on shares of big, broad, market cap weighted ETFs, such as the iShares MSCI Emerging Markets Index Fund (NYSEArca: EEM).

Thanks in part to our own Matt Hougan, that status quo changed and investors began digging deeper and started buying its cheaper, more representative cousin, the Vanguard MSCI Emerging Markets ETF (NYSEArca: VWO).

But did they dig deep enough?

It seems the answer to that question is very much a work in progress, as EEM and VWO still have a massive duopoly in the emerging market ETF space despite tracking the exact same index.

Fully 98 cents of every dollar in an emerging market total market equity fund is in VWO or EEM. Same goes for trading: the two funds get more than 98 percent of the daily volume of all funds in the segment.

But that doesn’t make them the best. Sure, they’re even easier to trade than many domestic ETFs, and the cost of trading them is minimal -- 3 basis points on average – which is a key consideration.

But are there better choices out there?

South Korea’s Status

One of the big dividing lines in the emerging markets space is what to do with South Korea.

MSCI considers the country to be an emerging market, while S&P and FTSE consider it to be developed (That may change on Wednesday, June 20, when MSCI unveils possible changes to its country classification list, with South Korea possibly in line to get promoted to developed market status.)

In any case, because VWO and EEM track an MSCI index, South Korea is included.

The $200 million SPDR S&P Emerging Markets ETF (NYSEArca: GMM) tracks an S&P emerging markets index that doesn’t include South Korea. Neither does the Schwab Emerging Markets Equity ETF (NYSEArca: SCHE), which tracks a FTSE emerging markets index weighted by market cap.

Instead of debating the relative merits of each argument determining whether South Korea is an emerging market or not, it’s really best to let the market tell us.

After all, it stands to reason that the millions of participants in global asset markets are better at determining the true classification of a country better than a small committee of Ivy League graduates.