I use Kaspersky Internet security on my iMac. I had Bitdefender but it used up a lot of resources in my opinion. Both were good. Even with MacsOSX you need security even if you are sending data to a website, smart practice.
I have run complete scans of my computer and had no problems with any software so far. I run a dual platform using Parallels, for those programs that suck on a mac.
No problems and I don't care what the DOJ says about Kaspersky. By the way, it is an interesting read about this guy.