In my ever so humble opinion..
MMF2 is more powerful in *almost* every aspect due to its age and exposure but is hindered by piss-poor, archaic designs that make for a generally unpleasant experience. Also, said "power" heavily relies on questionably stable 3rd party extensions and such; the program itself hasn't changed a whole lot since 1994. I'm serious.
CC might be a tad weaker here and there but is ultimately superior to MMF2 due to its thoughtful designs and features. However, it's kinda slow, often buggy, and lacks some the ease-of-use you'll find in C2. If it wasn't tied to Windows and abandoned I'd use nothing else.
C2..C2 is tricky. It's lightning-fast, clean, well-designed, and has lots of great features to make your life easier and development faster. I want to recommend it more than anything but I think HTML5 is holding it back considerably. You trade off expansive, powerful, feature-rich games and tools for, well, whatever you can cram into a smartphone or browser. In my opinion multi-platform support means nothing when it cripples everything else. (Hell I don't even think HTML5 REALLY means multi-platform..It can just run games in browsers, and all platforms support browsers..therefore HTML5 games run anywhere.) But of course "HTML5 is young and constantly growing"..I just think that by the time it really gets good, all the desired exporters and that which comes with them could've been finished already..but that's another topic..moving on..
Hopefully this helps and doesn't sound too biased; I've used both Clickteam & Scirra software extensively. It just comes down to whichever is more appropriate for you!