If you actually want to learn the underlying API then you should start off without one of the frameworks.
Learn it the way we did it all those years ago with Charles Petzold's book, Programming Windows. A really good foundation of knowledge of how windows and messages work will serve you well.
In the longer term, a good framework, e.g. WinForms, Qt, VCL etc. will increase productivity. But if you start with one of them, then you are in danger of not knowing the difference between sent and queued messages, not knowing the difference between an HWND, an HDC and a HANDLE, and so on.
A good framework, is great, but you'll get more out of it if you understand what's underneath it.
