There are almost as many striking methods as there are martial arts. Martial arts differ on even the essentials. One very heated argument: whether a fist should be executed horizontally (common in Karate, boxing, and most modern styles) or vertically (common in Wing Tsun, some Japanese and Chinese styles, and boxing around the turn of the century {From Si-Gung Keith Kernspecht's book On Single Combat}).
Some martial arts, such as phoenix-eye style (Chuka Shaolin), employ only a certain type of strike. In Chuka, for instance, only the phoenix-eye fist is employed, which is made by making a fist and then extending the first knuckle of the middle finger for use as a pressure point weapon.
Most striking methods in most martial arts follow the same basic tenet:
"Use hard to hit soft, and use soft to hit hard."
The meaning behind this axiom is that the key to successful striking is to internally damage the opponent. For instance, when striking the stomach or throat, which are soft areas, a fist or knife-hand should be employed because these will achieve greater penetration. Here, penetration does not imply that the skin is broken.
In contrast, if one is to hit the head, a punch would very likely damage one's own hand more than the target. Therefore, when striking the head, a palm strike is employed. This becomes more important in the later levels, when one can cause internal rupturing or unconsciousness through the transfer of vibration; when employing this technique, a greater surface area of contact means a better transfer of energy. Thus, the palm works better than the fist. Penetration is not the key, here; rather, delivery of a mushroom-shaped vibrating force that passes through the opponent.