Some great games have been made with MMF, Some great games have been made with C2 and GMS.
Out of the three and there are more in the list, I preferred GMS, and actually dreaded moving to C2.
Took me a week to settle in and haven't looked back.
My thoughts MMF started off with promise, but agree with Arima, C2 is everything MMF should have been. MMF is not friendly, it isn't easy, and has a steep learning curve.
The choice is rather between GMS and Construct 2 - each has its pro and cons and it is dependant on your project.
The only downside, and biggest frustration is exporting to various platforms (iOS and android).
If you want to build serious games, unity3d is the best - hands down, but for ease and simplicity C2 wins hands down.