In my experience unless you're throwing straight heat, the hammer style is actually more effective. Because the hitter is trying for his life to get around on your fastball, he's able to read the uncle charlie curveball and still get a blooper out of it.
They will often not even pick up the hard curveball until it's to late.
I've also found a hanging hard curveball is damaged much less than a slow one for me.
I think the hard curveball is just more effective in HS.
Last year I threw some great curves, fooled the hitter but too often he was able to drag his bat and get a blooper over my not so quick infielders.
If the hard curveball is not picked up right away the most they seem to get is a grounder to the shortstop.
Don't get me wrong, if you hang it, it will fly a long ways no matter what speed, it just seems the hard curve is less susceptible to giving up weak hits.