Noshow,
Most of what I know about BP/wings, I learned on this board or in Jablonski's DIR book. There are 100's of posts listing the virtues of the BP&W, and they seem to pretty accurate.
IMO the Balance is essentially a BP&W that doesn't have much flexibility.
1) If a person wants to dive doubles, the Balance is out of the running; the BP can be configured either way.
2) A SS backplate provides its own weight; I have to put weight in the back pockets (But when I go from a dive skin to a 3 mil, then to a 7 mil during the season or even during a dive trip, I can easily change the weights to change my "Balance". I believe you need tools to change the weight on a BP).
3) The BP&W requires a weight belt, but the Balance requires two weight pockets (and when weighted for a 7 mil suit, it's usually easier to take the pockets out to switch tanks).
4) The Balance has a stowable pocket, but you can buy pockets for the BP&W.
5) The quick-release shoulder harness buckles on the Balance are great for getting out of your gear (or getting someone else out of their gear in a rescue class), but they add two more failure points.
To make a long story short, If I had a BP&W, it would be configured exactly like my Balance is right now (except for the weight system). For 90% of my diving: 50F to 85F, 85 to 110 fsw, spearfishing, picture taking, sight-seeing. . . the Balance is everything I could ask for.
If I decided to dive doubles next month, I'd be wishing I'd bought the BP&W.