Heart.
I'm not sure. By "first", do you mean which comes first in time, or which is the more major source of guidance in decision making? I'm not sure which I listen to first in time, but as to which one I pay more attention to overall it depends on the situation. My thinking about truth and the world is definitely more heart-based than with most who are as analytical as me.
My heart speaks first but at a lower tone while my mind speaks later but louder. Depending on noise I hear them differently. Sometimes I stop and ask my heart when I find I didn't hear it.
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