NEW YORK ( TheStreet) -- As investors regain their appetite for risk in the wake of a global financial crisis, funds have been flowing into ETFs like iShares MSCI-Emerging Markets ( EEM) and SPDR Barclays Capital High Yield Bond ( JNK). A new series of mega-cap funds from iShares , however, may be part of a changing tide back towards quality. The three new nuanced mega-cap funds from iShares -- the Russell Top 200 Value Index Fund ( IWX), Russell Top 200 Index Fund ( IWL) and Russell Top 200 Growth Index Fund ( IWY) -- join an already crowded field of mega-cap choices. Among the most popular in the "mega-cap" category are the Vanguard Large Cap ETF ( VV) and iShares Russell 1000 ( IWB). While investors have been busy chasing the highest yields possible, it is important to keep quality at the core of your portfolio. Companies like Exxon Mobil ( XOM), Microsoft ( MSFT) and General Electric ( GE) tend to be well-diversified and hold up well during market fluctuations. The influx of assets into high-risk/high-yield ETFs is not sustainable over the long term, and investors should make sure they have solid mega-cap names in the core of their portfolios. One standout name among the mega-cap ETFs is PowerShares FTSE RAFI US 1000 ( PRF). While this fund is slightly more expensive and less liquid than better known funds like VV and IWB, its year-to-date performance make the price tag more than worthwhile. PRF has jumped 37.56% year to date as of Oct. 5, 2009, while IWB and VV advanced just 19.13% and 18.01% respectively. While PRF's 0.39% fee may seem daunting next to VV's 0.13% and IWB's 0.15%, the fund's multifaceted methodology is worth paying for. PRF uses an annually rebalanced passive approach to stock selection that breaks with traditional cap-weighted approaches. IWB, for instance, uses a traditional capitalization weighted strategy to select the relative weights of its underlying components. PRF measures mega-cap companies on the basis of four fundamental factors: dividends, book value, sales, and cash flow.