There is no easy answer for that ... At the moment C3 is C2 in a browser with some improvements.
C3 should offer a little better performance and better output, and it would be even better optimized when it will be updated with C3 runtime (at the moment is using the same runtime as C2).
There is also the problem of plugins, a lot of C2 plugins are not ported to C3.
Best is to try it for yourself and see how is working.
My opinion trough (seeing you have a pretty complex game and are getting ready to launch) is to stick at the moment with C2 and make the jump to C3 when it will be out of beta. Or finish this one in C2 and start the next one in C3.