"Best" is subjective since if you don't need it, how can someone do it better.
I will say that if you are sharing files with Windows machines (ftp, samba, what have you), Linux can "back up" the protection the Windows machines are running by re-scanning those files.
I always suggest clamAV, others like AvantGuard(?).
MacFee offers an official supported product but we have a hell of a time getting it to work properly.
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