Avira (even the free version) is a good solution for computers with not enough memory, specially notebooks.
Eset Smart security for the rest.
Having tested all the rest and never condidering cost, I strongly suggest these two, based on
proactive defense, stealth tech, and lowest possible usage of resources. Good for gamers too !
Note: for multimedia work it is wise not to be connected on the Internet and to disable the antivirus software.
Kaspersky (once was very good), Avast, Bitdefender, Norton and Zonelabs are also good but very heavy, drain resources too much. They are all similar and I think my criterion would be the user interface.
AVG, many "false positives" and hardly retrievable anything "killed" by AVG ! Leading to frequent re-installations
of Windows !
hope this helps...