which P2P is worse for bugs n hacks?

I've been having problems lately with viruses. My Norton can no longer get proper virus updates, and when I used Kazaa's Bullguard it found at least one trojan. I do download a lot of junk, video and audio files, program files (which I know are usually suspect), images, etc.

My main question is: which file share network is the worst for this kind of thing. And for that matter, which of the anti viruses is most effective. Do the main ones like Norton and Mcafee provide sufficient protection, or are the hackers always one step ahead?

I realize that this sort of question has been asked countless times on a website like this, but any and all advice would be really welcome.

Thanks