Marc,

Currently if I where to make the choice today, from a technical features standpoint, I would advise you to choose C# if you need any of the following:-

1] Include any unsafe/unmanaged code
2] Provide operator overloading in your classes
3] Have access to unsigned data types.

The next version of VB.NET addresses points 2 and 3 and I believe that a lot of people underestimate the need for point 1.

You will find C# easier if you have come from a C/C++ background but thats down to how comfortable you feel working with the language. Ultimately it all boils down to IL, not always the same IL though, there are some great MSFT blogs describing VB.NETs use of reflection to maintain some language features of VB 6.

Remember a bad algorithm is a bad algorithm irrespective of the language/compiler you develop it in.