I'd spring for Avast! personally.

I like Avast. Some people like AVG but I don't know if it's available for free anymore.

Some people just don't use any at all, but you must know what you are doing, such as:

-Not torrenting anything else than uncompressed mp3 files
-Avoiding visiting website link sections on old websites that are not maintained regularly, especially French websites.
-Not using IE

But even then you never know if you'll not fall onto a random software download site that seems to have a good reputation in Google but in fact hides viruses.

Just one thing about Avast. If it's an old computer, sometimes it might cause major slowdowns when Avast is updated (about once, twice or three times per day). I noticed Avast Update was rather CPU-intensive. X.x

AVG is a steaming pile of dung. It's malware itself, with its incessant ads for the paid-for version and the extreme effort it takes to completely remove. It also failed to remove half of the virii it detected.
I've used avast and it's at least somewhat decent as far as actually removing virii goes, but like all AV it's a giant resource hog.
These days I only use AV on a "by-need" basis without realtime protection - haven't seen a virus in one and a half years (and that one was a trojan in a keygen - should have known better)

the best virus protection is, obviously, to never use windows or mac. this won't take care of everything, but the vast majority of viruses are exclusive to those two operating systems.

the second best virus protection is to use a well constructed browser with flash blocking and other such abilities enabled. that way you can avoid client side scripting that traps you in endless popup loops or automatically saves and executes things on your computer.

the third best virus protection is to not be stupid in your browsing. don't click links randomly or jump to sites without checking them out beforehand.

the fourth best virus protection is antivirus software. if you take the measures above it really isn't needed, and virus software does take up quite a bit of your computer's resources. if you absolutely cannot go without it, though, then avast is what i would suggest, with malwarebytes for when things may get out of hand.

The issue about being careful what you click is hacked/deleted sites, though.

Eg: a few years ago, I visited a french TI website called TI-Center that I did not visit for a long while. I was global moderator there and I wanted to see if the author was still around. However, when I arrived on the forums and guestbooks, I got infected by malware because the site has been hacked. In such cases it's hard to tell.

I had the same problem happen when I visited WikiTI once, back before BrandonW started hosting it. Yes, viruses on WikiTI.

i went 2 years with out virus protection and never got a virus just by using safe net skills such as avoiding risky sites and such

i personally prefer avg as my antivirus of choice the free version is ok but lacking IMO go with avast for free its much better

also have heard alot about microsoft security essentials or something like that cant remember if it was free or how good it was though