Well, if you only plan to stick with one platform forever, I'd say VB.NET, but since C# is so similar to so many other language syntaxes, like java, sort of c++, and some other ones, I'd say C#. It's of course up to you, but it depends on whether or not you'd like to diversify in the future.
Another thing that some people like to point out is that at times C# has shorter syntax (less typing) for the same constructs you'd do in VB.net, but some people find the more verbose style of VB.Net easier to read. I can't comment on that myself, because I've been a developer for years, and I'm affine to C# personally. They're both good platforms, but I think C# gives you an overall wider lesson in programming that VB might.