I have a couple of J/B cues and as far as shape, I keep each of them somewhere between a nickle and flat. That way, I get the most tip on the ball.... less squirt because those super hard tips don't really grip the ball.
As for type of tips... I prefer something really hard like phenalic. But, the best I have is a super glue impregnated leather tip. The tip was soaked in a super glue solution for a long period of time and then installed on a phelanic ferrul. That thing is a monster. Every bit of energy is transferred to the cue ball.
Greg