Congrats on your Mewtwo.
I think the fast move you want depends on your play style. If you dodge a lot, you’ll probably want PC. That move is really quick but has much lower damage output. It does, however, build up energy faster, so you can fire off more Shadow Balls. Personally, I don’t bother dodging much these days unless it’s a charge move that announces itself well in advance of hitting. So I prefer Confusion for its superior power.
My Mewtwo is 76% (11/11/12) with C/SB and is currently at level 35. I love using it.