For me it's the curves. Women have a lot of curves: lips, cheek, forehead, neck, shoulder, back, waistline, butt, the bulge of belly over the womb area, thighs, calves, mound of Venus... Oh don't forget bust, some very special curves there. The first curve I usually notice is the waistline, so don't get too fat or it will disappear, it's something about the waist being narrower than the hips that separates the women from the boys. Even skinny girls have attractive feminine curves. Oolala!