It shouldn't matter which variation you pick (i think there's only one).
Adjust the sensitivity to your preferred setting.
I used the d-pad for more accuracy than the analog stick.
I've noticed you probably won't get it right away on the first man.
Probably by the 2nd or 3rd.
Make sure you are holding down the fire button to fire quickly.
Large Rocks will split into two, so hit them, and then pick off slightly
to the left and right.
If you hit the large rock to the side of the screen one of them will
break off and go offscreen and you won't be penalized.
There will be a string of smaller rocks that all come in a row. At some
point you will be able to shoot all these in a row.
Here's how I did it: