If you have good Excel experience/knowledge, VBA has a context for you that makes it a gentler introduction. VBA is a self-service language, and can readily be picked up by business bods who are using Excel, whereas the .Net languages are far more of a development tool and benefit from learning development paradigms, structures, and the paraphernalia that goes with it - hence the steeper learning curve.

Learning VB6 seems somewhat pointless to me. The language is the same as VBA, it just has a separate IDE (Visual Studio) and different ways of building, such as forms, but it is far more effectively dead than VBA is or ever will be. The .Net languages might be somewhat easier knowing VBA if developing Excel based solutions, but it is still a world away.

As for HTMl, that has no bearing on VBAor VB.Net/C#, but really for web based stuff you should be learning JavaScript as well.

What you look to learn should be driven by a specific need, which should in turn direct what is the best choice, otherwise you will get nowhere.