If you tweak both products for absolute maximum protection Kaspersky internet security will run rings around Bitdefender. Kaspersky's Application control is solid at default but once tweaked if offers amazing protection as does Trusted Application mode and the firewall if you tweak it correctly.
a few years ago i ran Bitdefender for a while and I came across a few bugs, that, when reported to them on their forums they didn't seem to care. I dropped it and tried it again about 6 months later and it was just buggy and, at the time Bitdefender's customer service was absolutely terrible. I don't know what Kaspersky's customer service is like as I've never had to contact them for anything.
Kaspersky has always been the better product in my opinion for years and years Kaspersky has consistently offered top notch security their products have just always been a cut above again, in my personal opinion. The only real problem Kaspersky had for a very long time was how heavy KIS was, it was pretty much unusable it was that heavy, but even that's changed now.