First of all, I feel ashamed of myself because I didn't know that LYN can support more than 10 poll choices

Okay, I'm not going to say it is the BEST, but kaspersky is indeed one of the antivirus that I trust the most. Here are the pros and cons for this AV

Pros:
- Very high (if not highest) detection rate
- Frequent virus definition update
- High speed when downloading definition (in comparison to antivir, which is extremely slow)
- Simple but somewhat atrractive user interface

Cons:
- Very slow scanning speed
- Affect OS operation when scanning for virus
- It's not free
- Relatively higher memory consumption in comparison to the like of Nod32, f-prot, antivir etc.

I believe it is not that serious for experienced user to use PC without antivirus
I can't remember when was the last time my PC infected with virus. Usually a full scan detects no virus.

But then again, it's better to be safe than sorry, I install antivirus just for safety sake and I don't see any big performance implication on the OS as dead__man said even though I'm using "heavy" antivirus like Kaspersky (it only affects system performance when I do a full scan, otherwise it is fine)

AVG Free is free for non-commercial use only
You still have to buy commercial license to be used legally in company.

For those who want to use free antivirus, I would suggest antivir

It doesn't have nice user interface but from my observation (in camparison to AVG and Avast), antivir detection rate is somehow higher...It consumes less resources than other free AV too.

It had slow update problem before, but I think it is solved already.