I'm a fan of the precision school of thought. If the "fancy" word means something different than the "common" word, then the "fancy" word is preferable.
I would say if the "fancy" word means something different than the "common" word, then the word that is closer in meaning to what you're trying to say is preferable.
And I would say if the common word's meaning encompasses the fancy words meaning, then the common word is better, unless the specific connotation and denotation of the fancy word is such that it means something materially difference.
And I would also say hey nonnie nonnie oodelali golly what a day. So there.