You will find answer on this question here, just look at forum, 3 years old bugs like ghost traffic or black screen on Windows boot and similar bugs. I used both, and Kaspersky definetly have less bugs/problems.
Clearly the ultimate way to check antivirus programs out is in their own support forums. I find BD slightly better than Kaspersky in the area that counts; identifying viruses. That's all I really care about beyond resource usage. But like Kaspersky, Bitdefender is not a cure-all. Malwarebytes beats both programs in Trojan detection and repair by miles. Registry repair after infection removal is where Kaspersky or Bitdefender fail miserably.
My rules for purchasing Antivirus programs are:
Watch the forums and look for repeating problems and complaints.
Look for response time on major issues.
Know that if the claims sound too good to be true, they probably are.
I look at the New (unknown) AV programs, it's how I originally found BD. The new guys tend to be more aggressive, cheaper and innovative. Though it's been awhile since I've seen any of those.
Never pay for more than a one year subscription at a time.
Never prepay. (Pay before the subscription has ended)
Never buy from the company directly, it is always more expensive.
That's in in a nutshell.