Generally speaking, the higher the BC the better. But you also have to figure the muzzle velocity. If (exaggerated here) you had a BC of 600 it would be better than the BC 500. But if you can't get the BC 600 going fast enough to start with, the lower BC 500 may be better. So each comparison is different.
Personally for the 30-06 and .308 rifle I have found the BC477 165 grain spire point boat tail bullet to be the most effecient out to about 400 yards, much further than the average hunting shot; but adequate for a long (400yd) shot. That's the max I have ever shot at a deer. Other than a few jump shots close in I have never missed a deer.
Shooter discipline is much more important than BC!!!!!
Cogito, ergo armatum sum