Ken did a nice, concise job of it.
It is a personal thing, and a lot of what is right depends on the intended use. Game guns tend to be neutral, competition guns a bit nose-heavy, and the live-bird guns I've brushed up against have been light up front - each correct for a purpose and feel.
I have two issues about balance.
One has to do with equating a hinge pin balance point with perfection, as it totally ignores the length of the frame. A 21 or a Parker has a long frame, and an Anson & Deely a short frame - apples & oranges. Some people reference the balance point from the front trigger, which I feel give you a better sense of where at least one of the supporting hands is working. Among my own guns, the easy handling ones have a balance point about 4.5" in front of the trigger. Once you get to about 4.75" or beyond, it's a little awkward for me in other than a clay target scenario.
The second is the matter of balance masking a gun's weight. To me, a heavy gun is heavy and a light gun is light. After that, balance defines whether it allows both hands to work conveniently or if it feels like you are shouldering a sledge hammer. A friend continually refers to his 8-pound field gun as being so well balanced that it feels like a 6 pound gun. Excuse me, but I don't get it. If I pick up an 8 pound gun, by gosh it feels like 8 pounds to me, whether all the weight is in the middle of the broomstick or equally distributed at either end.
