Colombian BCI can be good starter boas as long as you are prepared for the size they may attain. 6-8 feet is average, though its not common, but some females may exceed that. Hog Isle BCI can also be good choices and stay smaller (4-6+ feet), as well as Central Americans (usually around the same size as Hogs depending on locality, some may get slightly larger). These all are typically good feeders and very hardy and forgiving.
Sandboas and Rosy boas are awesome starter boids, but they don't do much in the preparation for a BCC. They are small and easy to keep provided they are kept dry.
Colombian Rainbow boas are good as long as you can keep the humidity up.
Dumerils boas can also be good, again if you are prepared for the size. Just make sure they are feeding well, as they can be stubborn feeders.
For more specific info on BCC, BCI, or any other Boa Constrictor subspecies, check out the Boa Constrictor Forum