I use and like Bitdefender. I have it installed on my media server because it has a lot of available RAM... Bitdefender uses a fair amount.. up to a full GIG for all its functions. I tried SOPHOS for a while and although it seems to do its job the program and its interface and functionality is largely cloud based which I found cumbersome and slow to deal with so I stopped using it.

I run AVAST free on my older PC (emailing, reading news etc). It does seem to provide good protection esp while visiting websites.. it often warns me about potential risks. Downside is that it often tries to up-sell it's paid for version with popups on my computer. It's pretty light on RAM useage though which is why I use it on my older PC with only 4 Gigs of RAM available.