Both are pretty useful, but however you fancy creating coding/events matters between programs.
MMF Uses a Event approach, with low-end coding ( ie, you have simple equations, not extremely long lines of CODE )
GM uses a drag-n-drop interface in conjuction with a very extensive coding language. even though the DND feature is pretty useful ( along the same line as MMF in the way it works ), you wouldnt get far without learning code.