U.S. stocks are looking scary after their worst year in a decade. Credit is risky too. Volatility is back. For many, cash and short-term debt may be the best place to go. As fund company executives, portfolio managers and strategists at some of the world’s biggest money managers turn to 2019, they’re cautioning that returns could be muted across asset classes. They’re also urging investors to be increasingly selective in the quest for value. Here’s a sampling of views.