I've used both PCs and Macs for a long time. It was at least 20 years ago now I had Norton in Windows for one year (that's how long the automatic definitions updates lasted with the purchase). It never found anything and slowed the computer to a crawl when active.
I have never used AV software since then on any computer I've owned. It's all about good computing habits:
- Never download software from untrusted sources.
- Never even think about download anything from P2P (peer to peer), pirate, or other file sharing sites.
- Never believe any site that says you need to download a Flash, Java, codec or other software directly from them. It is a lie 100% of the time. Anything you install from such prompts will be malware or adware.
- You can't even trust legal software aggregate sites. They all include adware that installs along with the freeware/shareware/demo software you download.
For number 4, what I do is use those to look up certain kinds of software I'm looking for. I then take their list of possible software I would like to try and look up the web site of the company who actually writes it, and download it directly from them.
Beyond that, there are no Mac viruses. Literally. None. Viruses are software that self replicate with no need for you to do anything to help that along. These do not exist, so there is nothing for AV software to look for.
There are tons of Trojans. That is any adware or malware that requires YOU to you to download and install it. It can't get on your Mac on its own. AV software cannot, and will not stop you from installing them. Making AV software, once again, completely useless.