Nice to see you're so enthusiastic about learning.
A couple of clarifications:
Java is a technology(framework) and a language
C# is just a language over the .Net framework
Since you are already familiar with VB
.net, you should already be somewhat familiar with the .Net framework, therefore, by taking a C# course, you would be consolidating your knowlege of the .Net framework, by going over the same framework APIs again, while learning a new language
On the other hand, by taking Java, you would be learning a new framework, a new technology, and a new language. Many of the features of the Java language are shared with C#, so by learning Java, you will be learning C#.
If I were in your position, I'd take java while applying the lessons learned by practicing them both in C# and Java.
Best of luck!