What is the best ever Antivirus Software ?

I suggest Avira AntiVir..I've been using it for almost three years and never had a problem with it..It doesn't use up too much RAM.. I also use a supplementary antivirus software: "Smart Virus Remover"..Quite useful..It specializes in deleting autorun viruses..It also has some features such as USB write-protecting and disabling of USB drives on a computer..

I've used Nod32 for a long time and my OS doesn't become slow. I think this antivirus software doesn't cost so many resources and is worth using.

I have heard good things about Kapersky.

I am using Microsoft Security Essentials (free to all Windows XP, Vista, and 7 users). It's been touted as using very little resources, and I'm here to attest to that. What a difference! I've used Norton and McAfee and they bogged down my computer every time they scanned and/or updated definitions. I'd have to suspend anything I was doing. One thing I do is set my scanning schedule for a time I know I won't be online. No disruptions on my time.

You could try Norton Gaming Edition. It's very lightweight because it's meant for gamers.

The one thing that I don't like about AVG, Norton, McAfee, etc is that they cost a lot, they're only good for 1 year, and they slow down my PC. So I gave 2 free antivirus software a try: Avira Antivir and Avast. For me, Avast is better because it doesn't slow down my PC and the update files are smaller (thus, faster to download) than Avira.

that's part of the deal with av scanning the scanner loads and scans the file before it goes to the app that is trying to open it. i use avg and am very satisfied. Norton is seriously resource hungry and doesn't catch all activity. avg has done all that for me. it runs background but not bad. i do scans manually instead of automatically. and it's web blocker works a-ok.

I have used Nod32, Panda AV, Kaspersk, Norton and ... that's all I remember. Norton is like a hungry beast it drains lot of systems free memory and the scan is slow. The Panda is a good antivirus software faster and lighter than Norton, maybe something between Nod32 and the others. I like it but personally my favorite is Nod32. I use it for 4-5 years now and I never ever have any problem with it. It's stable, reliable, fast and light. I recommended it to anyone who spend lot of time on the PC.