Just don't do the squats or deadlifts on the bosu ball...
We're talking about core, right? I've always been told squats and dead lifts are for buttocks.
Which is the best core strengthening exercise ?
if you can do them properly like all the way down
yeah basically put your body as parallel to the ground as you can without touching it, and not arching your butt up.
Saying you have to go flat is like saying that partial deadlifts (aka: rack pulls) do nothing.
not saying that partial excercises are useless
i would be one of the first to say you can get some strength increases including those excersises like jumping pull ups
even isometric excercises
all i was saying is that most guys will not be able to do them properly