I usually remove Mcafee, Norton, AVG (even paid version) and pretty much any free AV.
I found the Microsoft to be about the best for free, but still end up with bugs. Avast I find is worse than AVG these days.
I would happily recommend ESET Smart Security (firewall, Anti-spam, Antivirus, Anti-spyware) or ESET Nod32.
Cant find any other AV solution that uses less than 65MB RAM full the Full security suite. Have installed it on 170+ pc's in the last 18 months.
I have only had one return as the customers kid un-installed it as he could not download bit-torrents.