Since vb6 is unsupported by Microsoft these days, I can only assume you mean vb.net....
So this would depend on what area of coding you would like to learn. Native coding or .net coding, if you choose the .net path I suggest C# to be the better option, If it's native coding then C++ would be the one. There is no such thing as "one language is easier to learn than another language" Just put the time and effort into your learning and will be good. Btw just to help you choose a little better... If you intend to biuld GUI application then go with .net, If its hacks ect.. then native code will be the choice to make(meaning C++ or similar). If you want to be unique and really learn in the PE structure's then go assembly and do away with any high level languages. Dont assume its hard to code in assembly because in most cases for hacking ect... its actually easier