The idea that there could be a truly neutral source is not really realistic, human minds do not work that way and there are many other reasons why it's even harder than that.
As long as you stay away from the blatant extremes, partisans, people with some other stake in the game, etc., all you can do is evaluate relative bias, and try to adjust for it. It is inevitable that your take isn't going to be unbiased, either, but this way you'll have had a decent shot at minimizing wrongness.