In any given situation, especially when fighting within a close range to your opponent, a punch will be faster than a kick. Again, this is not always the case, but most of the time, a practitioner will be able to execute a punch faster than a kick.
To effectively execute a punch, you need to be able to see openings in your opponents defense, and you can practice those with specific timing drills in class. What I want to address right now is the technical aspect of the punch itself. Let me first start by saying that I've never really been a religious viewer of boxing matches, and in my opinion, the reason why I've never really enjoyed boxing is because as a fighter gets tired, their technique tends to drop off a bit. Even when each fighter is fresh during the first few rounds of a fight, I find that I have a "bone to pick" with the technique of many fighter's punches. In boxing, hook punches are often used fairly exclusively, and are executed by using an almost circular path. This causes the fighter to hit his or her opponent with the two smallest knuckles on the hand, which are, coincidentally, the two most vulnerable knuckles with which to strike. The reason why boxers can do this is because of the gloves that they wear. Gloves often soften the blow of punches, but in a real-world situation, you won't be asking your opponent to hold on a minute while you put on boxing gloves.
In the real world, the gloves will be off, and if you strike with the two smallest knuckles in your hand, you will most likely break those knuckles, causing more pain to yourself than pain to your opponent. Fortunately, there is a very easy way to correct this problem if you happen to find it happening in your training center. Here are three things you will want to keep in mind in guiding students to a more effective punch.
To cut down on hitting opponents with the two smallest knuckles in the hand, the first thing you have to watch is the trajectory of the punch. Start by having the practitioner place their tight fist on their side, with the palm side facing towards the ceiling. Ask them to execute a punch, and stop them immediately if you see them start to swing their punch outward. Instruct them to punch straight inward, and demonstrate this concept for them. It adds further credence to your point if you also make a point of saying that the shortest distance between two points is a straight line, making the straight punch significantly faster than the hook.
In my personal experience with untrained fighters, and even with some beginning their training, I've noticed that these practitioners rarely get the full rotation that is possible on their punch. Some fighter's punches will land on a punching bag and leave a vertical impression on the bag, while others will punch and leave about a 70 degree angular impression on the bag. As an instructor, you must stress that this is incorrect. When executed correctly, a practitioners punch should leave a horizontal impression on the bag, and when viewed from the front, the "palm" of the fist should be facing the floor.
3. Point of Impact
The point of impact, in my definition, is the point on the martial artist's body that is making contact with the assailant. In the straight middle punch, this point should be the two largest knuckles on the hand. Once you get the practitioner to the point where they are punching straight forward and their fist is in a horizontal position, tell them to pivot, or cock their wrist slightly outward. This will cause the two largest knuckles to protrude just a bit, emphasizing the correct point of impact.