Well I never will develop a graphics library like bgrabitmap and a widgetset like fpGUI, hopefully you and circular are here
Who is the best library depends on the user. I never used AggPas so I can't say.
I started using the default Canvas (PaintBox).
Then I used bgrabitmap to have transparency.
Of course I can program things by myself, to many years trying! But when something is already done I can use it to save time, like the whole Lazarus.
The things are programmed in the way the programmer things, I encountered software that I can't read and software readable, software easy to use and software impossible to understand for me. So if it's somewhat in the middle of easy and hard I can learn how to use it.