At the heart of your question is trim. Trim refers to the position your body will assume, and maintain, underwater.
When you're placing a lot of concentration through the viewfinder, good trim can make the job easy. Poor trim can make getting the shot difficult; as you body is forced into a different position by your poor trim, you will need to stop that motion with a lot of sculling with your hands and fins.
Given the basic building block of your body makeup, and your exposure protection, the other major items that affect trim are:
>Weights (their position and quantity)
>Air cell (type, location, size)
>Cylinder(s) and their size, position, material
I have a long slender build. For me, I have found that using a jacket, with a conventional weight belt, gives me excellent freedom in any axis. What little air is in the BC runs around to the highest point and stabilizes me there. I find this great for wide angle photography, where I am often contorted into odd positions.
I have no real experience with a back-inflate so I can't answer that as well as you may like. I do dive with a BP/W quite often, and since the air cell is on the back, it may be similar. I have found that my BP/W offers excellent stability in the face-down position, which is great for macro.
It's worth pointing out that if I use my jacket with the integrated weights, it places all the weight in front of my stomach, and will promptly roll me face-down. This is a function of weight position affecting trim.
In the same vein (weight placement and trim), I can vary the performance of my BP/W by the placement of the weights on my belt. Weights on the hips and back, my trim is pretty neutral, and I can easily roll; weights on the front, great for macro with face-down stability.
As you can see, there is more to this BC selection thing than meets the casual eye. An excellent starting point is energetically working on your awareness of trim underwater, and try a few different designs. As you get a better idea of what you want your BC to do, you'll also also know what to get for that task.
For me, I will choose my BC according to the dive at hand. Each tool has its strengths and weaknesses.
All the best, James
