Most of us long term users do not use AV software. Consider this. There are no Mac OS X viruses so if you run AV software it will download Windows virus definitions only. Windows viruses cannot install on the Unix operating systtem. Having said that there is malware and adware. Suggest you consider AdBlockPlus, Ghostery and Malwarebytes for Mac to combat these nasties.
As a general tip use wise browsing habits, avoid pirate and porn sites and do not download anything from softonic or CNET as, the same as Widnows, they include nasty little adware bugs. If you are to install Windows on your Mac, Bootcamp, VM etc., always install Windows AV software on that partition. Do a search of the forum about AV software.