This is one of the first issues a developer will face when making the commitment to begin working with the .Net platform. Which to use as your primary development language?
There may be external factors that will push you toward one choice over the other, such as standards in your workplace, a large legacy codebase of C++ or VB, or even the personal preference of your mentor. Since the .Net framework is shared by all .Net languages, it is essentially a toss-up. There are functional differences between the two languages, but they are minor. The good news is that the consistent .Net framework method names between both languages makes it relatively easy for a VB.Net programmer to read C# code, and for a C# programmer to read VB.Net code.
I prefer to work in VB.Net, simply because I have worked in Visual Basic for years and am very comfortable with that style of coding. That said, I can work in C# with only slightly more effort and I think you would find the same to be true. I have seen several surveys over the last year on this issue and developers are pretty evenly split among the two, with professional developers slightly in favor of C#, probably due to the strong presence of C++ code in commercial software applications.
If you have the freedom to make this choice yourself, then choose the language that you are most comfortable in and know that you are in good company with either choice. Learning to be productive in .Net application development is challenging enough, there is no need to complicate it with unnecessary worry about which language to work in.