Usually, to make it a little more simple, darker hair looks better with full eye brows/lighter with thinner. Also, it depends on how the person wears their hair. Having bangs or hair in your face would probably look better with fuller eyebrows, while hair pulled back or out of the face would look better with thinner, more 'dainty' eyebrows.
Also, if the person's nose is larger, fuller eyebrows would probably go better than thinner ones, and vice/versa for a smaller nose.
It all really depends on the face. There's no set preference for anyone, and nothing is sure to look good/bad.
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