My only experience with Bit Defender was with a recovery disc we used to try to clean TDSS off of a laptop. The live CD was able to remove the secondary malware (what was downloaded by the TDSS kit) and detected a TDSS infection, but couldn't remove the rootkit itself.
I used MalwareBytes to finish cleaning the system, after which BitDefender concurred that it was clean.
I was not impressed, though they show a good VB100 history since 10/2010.
IMO: If you depend on an AV to keep you safe, stay with what you trust.