I'm not using any anti-virus software myself. On my MacBook Pro, it's not necessary, and I'm also not running any on my Windows Vista machine. I mainly use my Windows Vista machine for photo editing and some light web browsing. As long as you don't visit dodgy websites and don't install strange software, I don't think the risk of getting a virus is very high. I do have a firewall setup properly. I don't like anti-virus software because it takes up resources and makes the computer slower.
On the computers of some of my friends, I've installed avast! anti-virus. It's free and works well enough, I've never seen a virus on their computers.
Back to actually answering a question (something that seems to happen less and less around here), I have used AVG for years and haven't had any problems. I also don't visit porn sites and open random emails. So that helps as well.
Well all answers to your queries are on this website Website this an antivirus comparison website It Compares them on various factors like speed ,detections etc.
BTW I am using NOD 32 pretty good detection and very Fast.