If you're not satisfied with NIS, many of the members use the below A/V's. Whether you have the trial or full version installed, downloading and running the Norton Removal Tool, is recommended prior to installing a different A/V.

Avira AntiVir Personal - FREE

Avast Free Antivirus

If you're looking to replace Norton with another suite, I'm sure you'll get varying opinions from other members.

Best of luck..