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!
Yeah, not to mention by the time HTML5 is good enough, other software may gain the upper hand by being just as good as C2 and having multi export...