The BCD you get should reflect what kind of diving you do, serviceability in your area, a solid weight release system and most importantly comfort.
The main benefits of back inflated BCDs are:
1) Fit - It doesn't squeeze when inflated, nor does it get loose at depth as you deflate. If it is a proper fit, the harness holds you comfortably the whole time.
2) Trim - A back bladder will help to stay more horizontal in the water with less effort... Because guess what.. air floats! On the surface you offset this by using some trim weight behind the BCD.
The main benefits of back inflated BCDs are:
1) Fit - It doesn't squeeze when inflated, nor does it get loose at depth as you deflate. If it is a proper fit, the harness holds you comfortably the whole time.
2) Trim - A back bladder will help to stay more horizontal in the water with less effort... Because guess what.. air floats! On the surface you offset this by using some trim weight behind the BCD.