MFC Pros and Cons

I currently know only the win32 api, should i learn MFC or would it be better to stick to the API?

There is no reason to go to MFC if you know pure API programming preety good. MFC exists only to make programming with C++ easier. I have read that is a bit slower than pure API.

It's not much slower, although the tradeoff is between ease of coding, and final size, since you'd need to distribute mfcxx.dll (for whatever version) with your program.

There are other classes in MFC, but these can be substituted by some better alternatives:

CString - string / wstring (both are faster and easier to use)

The controls are also basically worthless. If you want to use OOP for a windows app, just write a quick class for your window. I can send you one if you want (it's a bit cryptic, and actually looks very similar to MFC, but doesn't take loads of space).