Well construct classic and c2 are for different purposes IMO. CC is free, which is a nice advantage, and it has way more objects and behaviors, AND it runs faster and more efficiently. The cons are:
1: the interface, while similar, is just sightly more inelegant.
2: No box2d for physics -- as far as I can tell? -- so if you are interested in taking advantage of that, you'll have to integrate it yourself. That being said, you sound capable of doing so if need be.
3: Finally -- and by far most importantly -- CC games are direct-X, so they are, unfortunately, windows only, wheras C2 games can run on a myriad of platforms, including Windows and Mac, iOS products, android, and anything else that supports HTML five.
Basically, if you just want to make a showcase for your talent, and aren't worried bout restricting your audience somewhat, CC might be a better bet. If you want to distribute as widely as possible though -- and maybe even make some bucks off your work -- C2 is the way to go, as you can hit many, many more platforms. Now, if someone ever makes a CC exporter that allows it to run on iOS somehow...well, then the gap narrows, but until then C2 is where it's at. Also, I'm sure that, eventually, C2 will have most -- if not all and more -- of the features of CC.
Anyway, that's my two centavos.
Cheers,
Tiam