I've been using AVG for a few months and I am impressed by it, it stopped a Thus worm in it's tracks. However I had to use F-Secure online anti-virus to find a W32/Downloader and 2 TiBs entries, I was not happy. I've used NOD32 which was nice and I did use Kaspersky's once but it somehow screwed up windows, or rather I did while using it.

I also used Norton System works for the longest time but got rid of it after my last subscription ran out, major system hog and it's almost harder to get rid of than the viruses that it detects.
I'd go with NOD32, Bit Defender is kind of slow.
-Ray