I think bitdefender

Avast.

Avast

AVG Free Antivirus

MSE should be fine, or just none if you're careful. I use none on my PC and eset on my laptop (not free).

Comodo Internet Security

Both AVG and Avast are both good free anti-virus', but they are not great.

It's encouraged just to use common sense when browsing, downloading and sharing, but you will always be an easy target running Windows. Try Avira - lightweight, free, fast and secure.

Also, running anti-malware software by Malwarebytes once in a while, helps to keep you safe. It's also great if you are, or you suspect, that your security has been compromised.
http://www.malwarebytes.org/free/

I also recommend Avast.

Eset SS

Avasttttttttt!!!