Given that most markets were down (both in the US and internationally) in 2018 and the VIX (volatility indicator) peaked above 36 signalling a market bottom on December 24 of 2018, the US should be set for a decent year in 2019. How strong that is in the US depends on the Fed, China tariffs, and US domestic issues. Internationally may still have some concerns with economic slow downs in China and the EU.
Paul: I think it is difficult to make a blanket statement about all Exchange Traded Funds (ETF's) in 2019. It is safe to say that some will prosper in 2019 and others will lose value. The key will be to choose and select the ETF's that will increase in value. I recommend you seek professional advise from a Certified Financial Planner. A diversified portfolio is also recommended.