What is the difference in terms of speed & power between these punches?
All of these punches are good, but it's not about the most effective, it's more about the best punch for a given situation.
The Jab has more range than a Wing-Chun punch and also offers protection to your head, while your hand is extended. This is because of the rotation of 90° (or more, depending on who you train with) it lets your shoulder raise and protect your chin. The rotation also gives a bit more power, but also makes the punch more obvious, so that it is seen and blocked somewhat easier. A good jab should first move forward and then rotate, so it is less obvious. The forward and backward motion (getting punch back to your face) is the same.
The Wing-chun punch often starts a little bit lower than the head, while the other punches start and end on head-level. It goes exactly along the centre and has no rotation at all. It is more focused on relaxing right before and after the punch. The punch goes back on a lower level on the centre, so the other hand can punch the same level as before on the centre. It's very fast, with a lower range and no direct protection to the head. It's more about controlling the centre to have a good position to block/counter.
The picture of the corkscrew looks like a variation of the Jab with a 180° rotation, which gives more protection to the chin by raising the shoulder even higher.
I have also seen diagonal downward corkscrews for blocking low centre attacks. In this situation, the rotation helps with blocking and stopping the forward motion of the attacker.
I guess in Boxing range the Jab and Punch (Jab -> lead hand, Cross -> other hand) are the best for attacking, but if you fear getting countered while punching, it's better to use the corkscrew. Ata closer range where you can also use elbows, the Wing-chun punch is probably the best.
Be aware that a wing chun punch on average being faster and less powerful than a jab doesn't mean that it's not powerful enough, or that the jab would be slow. Also, you have fast jabs and power jabs, so it's hard to compare anyway.