UUP and the actively managed USDU, which includes some emerging market exposure, could deliver more upside in 2015 because investors are expecting the Federal Reserve to raise interest rates while other developed market central banks are actively moving to weaken their currencies.

For instance, the Bank of Japan is implementing policies centered on a weaker yen, and the stubbornly low inflation rate in the Eurozone leaves the European Central Bank more room for stimulus measures.

Additionally, the Swiss National Bank is racing the ECB to the bottom, purchasing euros to defend its franc currency. Switzerland relies on its export industries, so the country has been depreciating its currency in response to heavy safe-haven demand. http://www.etftrends.com/2014/12/improving-fundamentals-to-support-usd-etf/

UUP and USDU are up 11.4% and 8.1%, respectively, over the past year. UUP added $246.7 million in new assets over the past year, a total exceeded by just seven PowerShares ETFs.

ETF Trends editorial team contributed to this post.