I'm wondering what is the best whitening toothpaste?

Depends: The answer depends on what kind of activity do you want in your tootpaste. Is it antibacterial? Is it ancariogenic? Is it just pure whiteing activity? Will the whitening activity cause long term damage ot your enamel with all kind of abrasives that will thin out your enamel? The "whitening" toothpaste usually has abrasives and should be avoided to preserve the thickness of enamel.

Whitening toothpaste: All whitening toothpastes rely on being more abrasive to remove superficial stains from coffee, tea, cigarette smoke etc. They do not contain any whitening ingredients.While they may help initially, continued use can make the teeth darker as the outer lighter color is worn away revealing the darker inner structure. Also may make them more sensitive.