Well what arm angle do you throw from? If you're a low 3/4 to sidearm like me you have a natural break but, if you go over the top you have a natural sink.
If you throw from a lower angle I recommend a sinking pitch to throw people off but, if you are at a higher angle then you want a breaking pitch to throw people off. Just my thoughts.
I agree with the above poster though, make sure your arm is mature enough for whatever pitch you are throwing.
If you are willing to work really really hard I'd suggest a knuckleball but, don't throw one in a game until you can throw strikes with it and consistantly throw it well enough, it took me 6 years to throw one consistantly, I've worked on it since I was 9.