All depends on the THS condition and the bowler's style. I tend to carry a big ball, a medium and a small ball.
Yes, it is agreed that I could use the smaller weak piece and score fairly well right along with others playing on the lanes, but usually on the fresh shot, I'm going straighter with a big piece to properly break the lanes down right, and SCORE at the same time.
I then move in and ball down accordingly. But that's just me!