What is a good (and free!) antivirus for Vista Ultimate?

I have Vista Ultimate, and I tried tons of antiviruses, most of them saying that they need me to pay. Well, I tried OneCare, AVG, even RootKit, Panda and some others. Please, could you advise me on an antivirus for Vista Ultimate that's free, efficient and compatible? And please, tell me also WHY you would recommend that antivirus. Thanks!

What is a good (and free!) antivirus for Vista Ultimate?photoshop

bitdefender. the best nti-virus.

99.6% detectable rate. the best one out there.

What is a good (and free!) antivirus for Vista Ultimate?symatec

AVG should be compatible, if not then get free Zonealarm. Strongest firewall ever! 99% viruses come from the internet, and as long as you downlaod from legit websites, you are safe. Zonealarm even lets you let specific programs run with the inernet or not. dont be overwhelmed with te options, play around a little to get the hand of it. antivirus isnt really necassary unless you download ALOT of .exe files from the internet. Zonealarm should keep you safe till AVG is compatible with vista.
avast free home edition is free never had problem with them-