Hammer : is more for the forarm most forarm little bicep.
regular curl: more bicept little forarm
you should play with them and see how they feel..
Also in flex position look at your bicep look at your arm when in a hammer curl postion
and then rotate your hand and look at it in the other postion you will notice that the bicp with get longer and shorter...
so for so called peak you would work your bicep when the pinky is up tward you
not the hammer curl.
but i dont really think you can add peak, muscle just stays the same shape it jsut gets bigger...