Which one works better?

I was about to ask the same question. I mean which is the most effective agent; kojic acid, licorice, arbutin or glutathione?

This is not my opinion, just from what I had heard from other people. On the FAQ page of Diana Stalder products, they say

"Of the three products, the Papaya Kojic Beauty Bar is most effective at whitening, followed closely by the Black Beauty Bar, then the Licorice Beauty Bar.  The Licorice Beauty Bar is the mildest of the three, followed by the Black Beauty Bar and the Papaya Kojic Beauty Bar."

On another site I read

"Glutathione, or Gluta-C soap really works but it is a bit harsh for the skin.
Papaya kojic acid base soap/cream is the best whitening product available
in the market, online or over the counter alike."

Kojic acid is; however, carcinogenic.