I think Construct has more promise than GM and MMF. Technically I think it has a better architecture than the other two, Ashley is amazing, and it's open source so it has a good chance of taking off as it grows (personally I'm really amazed as how far it already is). But I think it really helps to have the perspective that TheInstance has. As long as Construct is in Beta then your games and your learning about Construct is in beta. It doesn't mean that if you are careful enough and work around any existing bugs and limitations you can't make a complete game, but I think you are better of at this point in Construct's life to focus on things like learning, experimenting, testing, and giving feedback.