which factor is the most important for adsense ads are targeted to site?

hi ,everyone
about adsense CPC
i have two questions:

1,
in adsense article:
How ads are targeted to your site
adsense say: they can put ads into my site in according to many factors, such as Contextual targeting,Personalized advertising…

i thnik contextual targeting is site niche, personalized advertising is visitor cookie

so i want to know
in both two factors :Contextual targeting,Personalized advertising
which factor is the more…

which factor is the most important for adsense ads are targeted to site?