C#
The .NET framework is cross platform now with Java. If you learn the .NET framework then you're able to write software for the majority of small/medium sized businesses. It's capable of enterprise software, SOAP/REST web APIs, and though I hate asp .net, ASP .NET MVC converted me from PHP for web development.
Also since there is a standardized IDE (Visual Studio), and standard package manager (NuGet) you don't have as many issues with project setup/etc like with Java. Hell the few times I've made Java spplications, the project setup part was probably the part that took the longest.
Worst case scenario, if you know C#, learning Java becomes much easier. It's really just a difference in namespaces/class names/design patterns; and the IDE.