BitmapSource vs Bitmap
I just want to say that Bitmap actually provides a super-fast means of doing pixel manipulation through the LockBits method of Bitmap. It is one of the fastest ways to create a bitmap if you want to do it by setting the pixels manually. Note that BitmapSource uses WIC while Bitmap uses GDI+. Due to this there should not be any difference (or a marginal at best) for loading or copying arrays of pixel data, and it is not a benefit of either Bitmapsource or Bitmap.
I would also add support to Bitmaps side, as it is a very old structure, with a lot of libraries accepting a Bitmap for editing.
The only benefit I see for BitmapSource is that it is a source for images in WPF and can be readily used.