best milk to use of these choices

I've never made kefir, but have ordered the grains & they
are coming.

My choices for milk at the moment are all organic,
1%, 2%, skim, all cows milk, and organic goat milk.

I'm wondering whats the best milk to use. I will be using
kefir as a probiotic so would like whatever produces the most strains of beneficial bacteria.

All the milk are pasteurized im sure, unfortunately.

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