Right now, C2 is very close to C1. The only thing you might notice in C1 is that it creates native application, so you can achieve native machine performance. However, with WebGL and the fact that computing power grow exponential every year and the fact that eventually personal computer and mobile phones will merge... Well, right now, we have tablets but soon, we will have something even smaller and more powerful, C2 will be better in the long run. You see now, that HTML5 is pretty much the bomb right now, and you see it almost anywhere but not everywhere yet.
Also, C1 is no longer supported and think about how long will it take to finish your game. In the long run, by that time, C2 will probably grow into something that will obsolete C1 completely given all the reasons above. You will surely have better usability and feasibility on C2.