Both of their respective hungers are insatiable, thus making them = in that respect.
However, in terms of 'hunger feats', Unicron actually devoured an entire universe + the stuff of space itself, on panel. Whereas Galactus could have potentially devoured all in existence, but stopped before even one universe was consumed.
So, as far as "who's eaten more" - Unicron ftw.
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"I am tired of Earth. These people.
I am tired of being caught in the tangle of their lives."
I've never seen anything that relates unicrons power level to his appetite. He simply devours to destroy.
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Humans are afraid of the dark.
And yet… At the same time, we’re fascinated and bewitched by it.
Maybe that’s why humans drink the darkness that is coffee.