I think the main difference is shyness.
My boa is not shy, nor is he head shy. If I'm in his cage he's right up there sniffing my hands, while my BP pretty much heads in the other direction.
Also when handling, a boa wants to climb and grip, while a BP wants to head for the ground as fast as possible. The boa is likely to find a comfy position and just hang out, while the BP will continue to try to get away.
That's my experience anyway.