I feel like I grew up in the thirties instead of the sixties but in all honesty, I turn to my husband first. He knows me best, he will never side with me when I am wrong and he looks at all angles. I will also ask my sister and my friends, my mom for certain things but I turn to him first. Defining "doubt" though would be helpful because it really does depend on the situation.
Generally, the person that knows me best is me. I look inwards before I look any where else. I feel it in my gut if I am making the right decision or the wrong one. Now and then, I take a poll and I ask everyone, all my friends. It helps me to think things though out loud but I usually end up with my first initial gut reaction.