Best AV, that is hard, I pick AV based on the circumstances (OS, user, risk assessment). Like you do not take a raincoat during a summer day.
The best AV was AVG Free (old version), it was great until they included all the garbage.
Bitdefender Free (old version) was also a goodie, until the new version came out.
For a little updated ones, there is not much of a choice for me, I use free only:
1. Kaspersky Free - great detection, light, you can setup virtually anything, unlike in any other.
2. Panda Cloud Free - super light, if you have got a reliable connection, there is not a better alternative.
But if given an option Emsisoft would be my paid choice. It is user dependant, I love everything about Emsisoft.