What is the present AV engine version in bitdefender and other AV which is using bit defender engine?
According to AV-Comparatives, Bitdefender itself has better detection than AVs using its engine, like Quihoo 360. So probably better to stick to the original.
If you are talking about the real-world protection test, the differences can be due to the webfilter. Products licensing the Bitdefender engine don't use Bitdefender's webfilter.