Jab is most impotant punch in boxing. Essentially those three clips show much the same punch, just at different targets.
Try not to over complicate the jab. A jab to the stomach, a jab to the chest, a jab to the head... its still a jab, you know?
In terms of doing a jab quickly, I found nothing was better than the punch bag and explosive lifts with lighter weights. It worked for me.
The thing to work on is form though. Your jab must be powerful and fully developed, using full extension of the arm. A good jab will win you a fight more than any other punch. It sets up power shots, keeps your opponent off balance, keeps your opponent defensive, protects your chin... it has so many uses.
Regarding your videos, (and bearing in mind what I said above) what do you think the advantages to each are? I know what they were to me (one in particular) but I want you to think how you could use it. If you think about what you can do with them, you can apply that quicker in the ring than what someone is telling you. That is my experience.
And in that ring, you have to figure it out yourself. It's a good habit to get into.
"Let your food be your medicine, and your medicine be your food"