MMGames
You decide:
C3 editor has lots of new features and tools, but there is almost nothing new that you can add to the final game. So no, you can't make a better game in C3, comparing to C2.
C3 can export for mobile, but as I understand, it only works for selected platforms.
C3 is still a fairly young software and there are lots of bugs and problems with it.
Many popular C2 plugins have not been ported to C3 yet.
C2 will not be getting any new feature updates, only bug fixes.