Benzoyl Peroxide.

Why?

It kills all acne causing bacteria and will kill the bacteria in the pimple.

Benzoil. I have tried both. Hydrogen burns just as much and does not have the effectiveness or longevity of the benzoil peroxide.

Agreed with above posters. Hydrogen peroxide disinfects but does not kill p.acnes.

H2O2 is good for cleaning wounds but BP is going to be better for treating acne so depends a little on what you're trying to achieve....

Hydrogen peroxide solution (3%) liberates oxygen when in contact with catalase present on wound surfaces and mucous membranes. The effervescent action mechanically helps remove pus and cellular debris from the wounds and is valuable for cleaning and deodorizing infected tissue. The antimicrobial action is of short duration and is limited to the superficial layer of the applied surface because there is no penetration of the tissue.
[Aiello, S.E. (ed). The Merck Veterinary Manual. 8th ed. Merck & Co., Inc., National Publishing Inc., Philadelphia, PA. 1998., p. 1848] **PEER REVIEWED**

HP made my pimples even more red and while they vanished relatively quickly (3-4 days), they left behind flat red scars. And I was not picking those pimples either. So far, BP has worked better (preventing new zits and reducing existing acne scars) BUT takes more time to kill present pimples.

HP always resulted in a longer healing time. More skin peeling and things...scarring was not permanent. BP always just burns a hole in my face. It's brutal...and doesn't really work that well, if you ask me.
Try Mario Badescu Drying Lotion...I read incredible reviews on it. Finally, I tried it...my new holy grail. It works.