I have this from someone who I consider one of the most knowledgeable people in this area, although he qualifies it by saying his memory is dragging it out from 1969!
"The rounded tip produces less drag and is mainly employed on the lower powered engine whereas the square tip allows a wider chord, a smaller radius and, whilst generating more drag, produces/permits/absorbs (not sure which) more power before the tip goes supersonic".
As he says, a long time ago, so file under "not wholly reliable"