How do you pick the size of ball you choose to ...

I think that it's really just what you find comfortable.  For me, I have to find a ball with the right weight for me, and with finger holes that fit well.  If you do this, I would just stick with that ball and try to improve on your style form there.  Just finding the right ball for you and sticking with it is key.  Good luck.

You are the one person that knows what is the best weight for you. one that you throw that you can not hurt yourself and you feel comfortable with. I throw a14 lb ball because that is what i can throw with out hurting myself and I can feel good after I bowl. think positive and good luck.