Well, in my opinion, I'd say it's a little more complex then that. "Riding bareback" for malware protection on the Mac is akin to playing Russian roulette with a 600 chambered cylinder on a revolver. Sure you have less of a chance of being infected but you still can be infected. As for myself, I use one of the free malware checkers currently available. I did some research using these 2 references online:
https://www.av-test.org/en/news/new...-attack-10-security-packages-put-to-the-test/
http://www.tomsguide.com/us/best-antivirus,review-2588-6.html
From these sites I'd say Bitdefender is the best, but you do have to pay for it. If you are worried about a system hit on performance this one would be the best choice. However if you happen to own a faster and/or newer Mac and don't want to pay a yearly fee on the off chance you might get infected, I'd say go with either Avira or Avast. They're both free and their system performance impact is fairly minimal.
Note: One caveat... If you do decide to load one of these programs, I suggest after you do so, when you perform any system updates that require a reboot, to disable real-time protection until after the reboot. I corrupted the malware program I was using by forgetting to do so. Fortunately all I had to do was uninstall and reinstall it.
Update: As of 12/17/2015 AV-TEST just released an updated report for Mac malware apps:
https://www.av-test.org/en/news/new...ac-os-x-13-security-packages-put-to-the-test/
Per this report it appears that a new entry, Sophos, holds a slight advantage over Avira as far as the system penalty is concerned. Also it now appears that Avast has dropped to dead last in the system penalty tests. All three of the afore mentioned apps are free. Symantec now joins Bitdefender as the least intrusive for a system penalty for paid Mac malware apps. It's interesting to note that Symantec and Bitdefender have a 10% system hit, Sophos has a 20% penalty, Avira has a 40% penalty, and Avast is close to 180%.
All five of the apps achieved a 100% malware detection rate. So it now appears that Symantec and Bitdefender are the best paid malware detection apps and Sophos and Avira are the best free ones. Unfortunately I'd say Avast is no longer a contender because of their new system penalty rating.