The translation, "like a son of the gods" takes away nothing from the identity of the fourth man in the furnace. The words of a pagan king don't define who that person was. They only convey his perception.
Perhaps a comparison will help... I'm a relatively-tall person, but not unusually tall by any means. A child once looked up at me and said, "Mommy, there's a giant in here!" (yes, there was plenty of laughter). Does her perception of me as a giant change the truth about my height? Of course not. Similarly, Nebuchadnezzar's perception of the fourth man tells us that man was unusual, but doesn't define who he/He actually was.
My faith in Christ and certainty of the reliability and truthfulness of Scripture isn't challenged one iota on this matter, regardless of what King Neb actually said, and regardless of whether it was Jesus or an angel. Personally, I think "son of the gods" makes more sense, given the context. In similar fashion, the centurion's words in Matthew 27:54 and Mark 15:39 could legitimately be either "the Son of God" or "the son of a god". It's the same issue, and the testimony of a pagan is not the rock on which my faith is built.